MOTOR CONTROL - FINALS

PT

A _ is a voltage step-down transformer which decreases the voltage of a high voltage circuit to a lower level with the purpose of measurement. These are connected in parallel with the line to be monitored.

low voltage

A __ switchgear has a rating of 0 up to 1kv.

high voltage

A ____ switchgear has a rating of more than 52kV to 750kV .

conservator tank

A ______ acts as a reservoir for the transformer insulating oil. It also provides and space if the volume of the transformer oil expands due to rise in ambient temperature and increase in load

medium voltage

A ______ switchgear has a rating of more than 1kV to 52kV.

Pulse Technique

A fast pulse of 500V AC is given to the transformer and taken both at the input and output in each phase.

Blast effect

A gas blast that is directed along the discharge or oil that is forced into the contact space may easily sweep away and replace ionized particles between contacts by deionized particles, causing dielectric strength of the medium to increase considerably.

Frequency Sweep Technique

A low voltage sweep generator is used and it is synchronized with a level meter for each phase to register a frequency response plot. The result is a graph that correlates frequencies in horizontal axis and attenuations per phase in vertical axis.

Inverse Definite Minimum Time Relay

A relay whose operating time is approximately proportional to the fault current is called an IDMT relay. Adjust the time delay setting to maintain the operating time of the relay. IDMT relays use electromagnetic cores because they can easily saturate currents larger than the pickup current. Relays are used to protect power lines.

overcurrent

An ______ is basically when the current exceeds its rated value. It may be from overload, ground fault, or short- circuit.

Insulation Test Pressure Test Contact Resistance Test

BUS BAR TEST PROCEDURE

electrical bus bar

Characterized as a conduit or a group of conductors used for collecting electric power from the incoming feeders and distributes them to outgoing feeders.

Cooling the arc

Deionization of the medium between the contacts is expedited by cooling and increases arc resistance. This may be obtained through the gas blast which forces a cooling element along the arc.

Insulation Resistance Test Recovery Voltage Measurement (RVM) Capacitance/Tan Delta Test Partial Discharge Test Breakdown Voltage Test

Dielectric System Tests

Fused Disconnect Switches

Disconnect switches can protect overcurrent ranging from 30 to 6000 amps, that might be utilized on service hardware, panelboard, switchboards, and motor branch circuits. These switches are used for disengagement methods for an engine. It tends to be utilized as motor controller.

Splitting the arc

Dividing the arc into smaller arcs may also increases the arc resistance as each arc is affected by separate lengthening and cooling. This may be done by adding conducting plates between the contacts.

ARC-QUENCHING METHOD

Heavy current flows through contacts of the circuit breaker when short circuit occurs before it is opened by the OCPD. When contacts begin separating, large fault current may cause increase in current density and temperature. Heat produced between contacts may ionize or vaporize the medium between which is usually air or oil. This ionized medium acts as the conductor and enables arc to occur between contacts.

Article110.26(A)(1)(c)ExistingBuildings

If electrical equipment is being replaced, Condition 2 working space is permitted between dead front switch boards, switchgear, panelboards, or motor control centers located across the aisle from each other where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the aisle from being open at the same time, and only authorized, qualified persons will service the installation.

High pressure

Increasing the pressure within the vicinity of the arc results to the increase of the density of the particles comprising the discharge. This causes the increase in dielectric strength of the medium since the increased density of the particles also cause higher rate of deionization.

Potential Transformers

It is used to step down the voltage of power system to a value which can be safe to be fed to low ratings meters and relays. The potential transformer is connected in parallel with the power circuit. The primary current depends on secondary burden. The one terminal of secondary of the potential transformer is earthed for safety.

Laminated Core Windings Insulating Materials Tap Changer Conservator Breather Cooling Tubes Buchholz Relay Explosion Vent

Main parts of the transformer

Lengthening the gap

Opening the contacts rapidly may increase the dielectric strength of the medium since this is directly proportional to the length of the gap between the contacts.

Recovery Voltage Measurement (RVM)

Other approach to get a generic knowledge of the dielectric status inside the transformer (paper-oil) is with recovery voltage testing. This test is used to obtain the polarization spectrum of the dielectric mixing information both of dissolved humidity and components degeneration.

Electromagnetic or Wound Type Conventional Potential Transformer Capacitive Voltage Transformers Optical Potential Transformers

Outdoor Potential Transformers

Partial Discharge Test

Partial discharge are small discharges that appear inside of the dielectric as a sign of its degeneration. They appear because of the increase of the electric field in small gaseous voids inside the oil and inside the paper, epoxy or as a result of the presence of metallic contamination, etc. There are two usual detection systems, acoustic and electric. Acoustic system seeks sound mechanic manifestation in ultrasonic range of discharges even enabling echolocation. Electric systems should allow determinate discharges and correlate them with another parameters. This test can be made online or offline if a source apart is used to energize the machine. In this test, it is important again to take note of the temperature of the machine and environment conditions.

Power Transformers Instrument Transformer Circuit Breakers Disconnect Switch High Voltage Bus Lightning Arresters Relays Capacitor Banks Substation Batteries Insulators Switchgears

Parts of electrical substation

Reducing cross section area of the arc

Reducing the area of the cross section of the arc increases the voltage necessary to maintain the arc therefore the resistance of the arc path is also increased. Smaller area of contacts or passing arc through narrow openings will successfully reduce the cross section of the arc.

Non-Fused Disconnect Switches

Same as fused disconnect switches, however non- fused disconnect switches would have a less protection against overcurrent and other electrical mishaps. Non-fused disconnect switches are not advisable for high voltage applications. It can be used as motor controller.

Article 110.26 (D) Illumination

Service equipment, switchboards, switchgear, and panelboards, as well as motor control centers located indoors must have illumination located indoors controlled by manual means; automatic control without manual control isn't permitted.

Article110.26(E)(2)(a)InstallationRequirement

Switchboards, switchgear, panel boards, and motor control centers installed outdoors must be: (1) Installed in identified enclosures (2) Protected from accidental contact by unauthorized personnel, or by vehicular traffic (3) Protected by accidental spillage or leakage from piping systems.

Article 110.26 (E) Dedicated Equipment Space

Switchboards, switchgear, panel boards, and motor control centers must have dedicated equipment space and be protected from damage.

Article110.26(E)(2)(b)WorkSpace

Switchboards, switchgear, panelboards, and motor control centers installed outdoors must have sufficient working space clearance in accordance with 110.26(A). No architectural appurtenance or other equipment is permitted in the work space.

Article110.16(A)Arc-FlashHazardWarningLabel

Switchboards, switchgear, panelboards, industrial control panels, meter socket enclosures, and motor control centers in other than dwelling units must be marked to warn qualified persons of the danger associated with an arc flash from short circuits or ground faults. The arc flash hazard warning marking must be permanently affixed, have sufficient durability to withstand the environment involved, and be clearly visible to qualified persons before they examine, adjust, service, or perform maintenance on the equipment.

1. review the equipment history 2. review the documentations 3. conduct visual inspections, thermal scanning, partial discharge testing, and kinds of tests. 4. prepare an inventory of the materials required for the materials, and order them, allotting thereto adequate lead time. 5. Develop a specific work plan and schedule. 6. to conduct a tailgate safety meeting, so that each person becomes aware of any dangers, special circumstances, and related work assignments.

Switchgear and Controlgear Routine Maintenance Prior to the outage, the following procedures must be observed:

1.Air 2.SulphurHexafluoride(SF6) 3.Epoxy 4.Silicone (Two-Part) 5.Silicone (One-Part) 6.Oil

TYPES OF HIGH VOLTAGE INSULATION

breather

The ____ filters the air that may contain dirt and controls the moisture level inside during the breathing process which can cause damage to the transformer. Silica gels are commonly used as breathers as absorbers. It ensures that only dry air can enter the transformer.

insulation resistance test

The _______ consists of measuring the insulation resistance of a device under test, while phase and neutral are short circuited together. The measured resistance must be higher than the indicated limit from the international standards. A megohmmeter or insulation resistance tester is then used to measure the ohmic value of an insulator under a direct voltage of great stability, generally 50, 100, 250, 500, or 1000 VDC. The ohmic value of the resistance is expressed in megohms. To conform to specific standards, the insulation resistance test can be performed under voltages of up to 1500 VDC. Due to the stability of the voltage source, it is possible to adjust the test voltage by steps of 1 volt. The stability of the voltage is critical; a non-regulated voltage will drop sharply in presence of a bad insulation which will cause an erroneous measurement.

Frequency Response Analysis Testing

The main purpose of this test is to determinate the frequency response graph of the equivalent electric/dielectric/magnetic/ mechanic altogether evaluated. There are two approaches to this test. Both techniques give the "signature" of the transformer with the inside information of the complete electric/dielectric/magnetic/mechanic status. This test is very useful as a complement of the usual tests and can also check that no alterations were derived from transportation, loose windings or displaced, problems in the magnetic core, etc.

Lengthening the arc

The resistance of any conductor is increased by also increasing its length. Likewise, arc resistance is directly proportional to its length. In this application, the gap between the contacts acts as the conductor so that when this gap is increased the arc resistance also increases.

Breakdown Voltage Test

The test is based in the insertion of electrodes immersed in oil of an increasing voltage up to when discharge happens. The test is repeated six times to get a repeatable measurement. The only disadvantage is that it is necessary to extract from the transformer a significant sample from 350 to 600ml.

Instantaneous Trip Circuit Breakers

These are circuit breakers without over-burden (warm) security ability. It is proposed to give just branch circuit, short out and ground security for individual motor branch circuits. It may not be utilized to give fundamental, motor feeder, motor over-burden, general branch circuit or gathering engine security. Since it is perceived, not recorded, it can't be utilized with free control. NEC® 430.52 necessitates that it will just be utilized as a feature of a recorded blend controller. Instantaneous Trip Circuit Breakers are shorted out in order to combine with a motor controller and over-current protection device. It isn't named with an intruding on rating without anyone else

Branch Circuit Fuses

These are fuses that can't be supplant with breakers with lower voltage rating.These are fuses utilized in engine branch short out and ground blame assurance. Instances of branch circuit wires are Class L, RK1, RK5, T, J, K1, K5, G, H, CC, and attachment wires. Intruding on appraisals go from 10,000 amps to 300,000 amps. It may be used for motor branch short circuit and ground fault protection. It can also be used as motor controller or for overload protection, depending on time fuse.

Pullout Switches

These are switches from 30 to 200 amps at 600V or less. Pullout switches with torque appraisals are appropriate for motor disconnection intends to meet NEC® 430.109, and all in all utilization for panelboards, switchboards, etc. It might be utilized as both an engine detaching implies and a motor controller to meet NEC® 430.111. Pullout switches with amp evaluations just are appropriate for general utilize just, not motor circuits. It might be utilized just in a motor circuit

Thermal Magnetic (Inverse Time) Circuit Breakers

These circuit breakers are planned to give branch, feeder, and primary protection, with intruding on evaluations from 5,000 to 200,000 amps. Appropriately estimated inverse time circuit breakers are expected to give motor branch circuit short out and ground blame assurance. It might be utilized for gathering motor insurance just when the electrical switch is tried, recorded and stamped {430.53(C)} for gathering establishment (see 430.53(A) and (B) for special cases). There are no circuit breakers recorded for gathering motor safety aside from HVAC applications.

Low Resistance or Current Zero Method

This method is only applicable for AC circuit interruption due to the natural current zero. This is an advantage of AC circuits for arc interruption.

Short Circuit Voltage

This parameter is usually expressed in % and identified in the nameplate of the transformer. It is the extrapolated result from the test voltage to 6 nominal voltage and should be near the protocol /nameplate value from the transformer. Its change will indicate irregularities in the magnetic core, winding displacement, short-circuits, mechanical deformations.

Definite Time Over Current Relay

This relay collects current values by applying an intentional time delay after crossing pick up value. The definite time overcurrent relay can be adjusted to generate a trip output at the correct time after it picks up. Therefore, time adjustment and pickup adjustment have time settings.

Extremely Inverse Relay

This relay is used to protect cables, transformers, and so on. If the pickup value of the current exceeds the relay set time, the relay can operate immediately. Relays provide faster operation even under fault currents. It is used to detect overheating of the machine. Extremely Inverse Relay are used in distribution networks and power stations. Relays provide fast operation in fault conditions due to their fault time characteristics.

Winding Resistance Test

This test determines the pure ohmic resistance from each phase windings both in high and low voltage and it exist a tap changer in each position. The high inductive character of power transformers implicates magnetization time and measurement stabilization should be taken under account while determination the measurement end and give the results. This has more relevance in high power transformers or from special designs or configurations.

Insulation Resistance Test

This test is performed on a measuring tester, able to generate high continuous voltages usually of 5000V that applied between both dielectric terminals of the power transformer, one terminal to all the bushings joined in high voltage, the other to low voltage and ground, and allows evaluating the punctual dielectric status inside. The tester has a high voltage tester operating from batteries or from the main. Measuring principle is based in measuring current/voltage in a continuous way that evolves as an answer to a voltage step.

Capacitance/Tan Delta Test

This test uses AC and pursues to know the loss angle of the tested element. This measurement technique is off-line although there are systems that allow an on-line approach. This measurement includes information of the moisture and contamination degree and emulates the behavior and voltage aggressions like the service ones. It is important to take note of the transformer temperature and environmental moisture.

Load Test

This test usually known as short circuit test. It is based in the insertion of a voltage in one winding (high voltage one) with the other winding short-circuited. This test simulated the factory one but it's not at all comparable in results because of not flowing nominal values. It is usual to register nominal and extreme positions if the transformer had an OLTC.

Very Inverse Relay

This type of relay is used in feeders and long transmission lines. Very Inverse relays are used in places where the magnitude of the short-circuit current drops sharply because they are far from the source. It is used to detect fault currents that deviate from the fault location.

Outdoor Potential Transformers Indoor Potential Transformers

Types of Potential Transformers

Fuse Holders

When utilized with motor disconnecting means implies and properly measured branch circuit wires, fuse holders may give primary, feeder, branch circuit, engine, engine circuit, and gathering motor protection.

Explosion vents

___ are used to expel boiling oil inside the transformer caused by faults to avoid damage to the transformer.

Connection group

___ can also be checked with the previous results and aided with voltage diphase between high/low voltage.

Excitation Current

____ is the current flowing into the high voltage winding with the low voltage side open. This current should be proportional to the no-load acceptance test but with the difference resultant from the use of test voltages different from nominal values.

Cooling

____ particles enable a more rapid natural combination of ionized particles so this also causes the increase of medium dielectric strength.

Buchholz relay

_____ is a protection relay used in transformers having a rating higher than 500KVA. It protects the transformer from electrical faults that occurs inside the transformer. The transformer oil gets decomposed whenever a fault occurs. It starts to operate when the transformer oil depletes and when gas bubble forms inside the transformer.

Pressure test, or High Voltage test,

_____ is performed to evaluate the busbar's capability to withstand to higher rated voltage. Pressure test is performed by applying two times plus two kilovolts DC of the system voltage to phase-to- ground for 15 minutes.

switchgear and control gear 1

all electrical components and devices that are used to activate, deactivate, and protect electrical consumers. Typically, switchgear is used in power distribution applications, while controlgear is used in industrial applications to control and protect equipment, especially electric motors, from surges, earth faults and short circuits. IEC 60947

Manual Motor Controllers

also called MMPs, regularly consolidate an attractive short out outing and customizable motor over-current protection. Its planned to give motor over-current protection per NEC® 430.32. Leeway separations are normally not as extraordinary as required in UL 489, and along these lines it can't be recorded as an electrical switch. MMPs can't give motor branch circuit short out and ground blame security.

HighResistanceMethod

arc is controlled by increasing arc resistance with time so current may be reduced to a value wherein heat formed is insufficient for the maintenance of the arc and thus extinguish it. Hence, current is interrupted, and arc is extinguished without the risk of damage to circuit breaker compartment. It is only used in DC and low capacity AC circuit breakers because of the large heat dissipation.

Switchgears

are composed of disconnect switches, fuses or circuit breakers that are used to for protection and control and to be able to isolate electrical equipment. One of its functions is to carry, make and break the normal load current like the function of a switch. In normal operations, it allows to switch on or off generators, distributors, transmission lines and other electrical equipment.

Power transformers

are devices that step-down transmission and sub-transmission voltages to distribution voltages. The ratio of primary windings to secondary windings determines the voltage reduction. This ratio can be adjusted up or down with tap changers located on primary and/or secondary windings. A no-load tap changer can only be adjusted when the transformer is de-energized while a load tap changer (LTC) can be adjusted under load current. Nearly all power transformers are liquid filled, but new applications using extruded cable technology have recently made dry-type power transformers available

Self-Protected Type E Combination Starters

are frequently called "Coordinated protected starters" and "Type E" starters. It is proposed to give motor over-burden and motor branch circuit short out and ground fault protection by joining a magnetic short circuit trip and adjustable motor over-current protection A "Type E" starter is a recorded blend starter appropriate for use without extra branch circuit impede and is restricted to single engine circuits. A self-ensured, type E, blend starter set apart with a slice voltage rating is constrained to use on unequivocally grounded wye type frameworks just per the gadget posting.

Instrument Transformers

are high accuracy electrical devices used in isolating or transforming voltage or current levels typically used to step-down high voltage and current levels which are associated with power transmission and distribution systems

Motor control centers

are simply physical groupings of combination starters in one assembly. A combination starter is a single enclosure containing the motor starter, fuses or circuit breaker, and a device for disconnecting power.

Circuit breakers

are switches that closes or opens circuits when a fault occurs in the system. In the circuit breaker it has contacts which are off in normal conditions but when a fault occurs in the system, a relay will send a signal to trip circuit breaker and the contacts of the circuit breaker will move apart. Classification of circuit breakers are based on continuous rating, interruption rating, insulating medium, and tank potential. Continuous rating is the continuous current that can flow through the device without overheating. Interruption rating is the largest amount of fault current that can be interrupted

Capacitive Voltage Transformers (CVTs)

are used for above 33kV voltage level applications. They are capacitive voltage dividers connected between the phase of main line and ground.

Current transformers

are used for measuring alternating electric currents. A current transformer produces a reduced current accurately proportional to the current in the circuit when current in the circuit is too high to apply directly to measuring instruments. The current transformer is connected in series with the power circuit. The Primary current of the circuit transformer depends on power circuit current. One terminal of the secondary is earthed to avoid the insulation break down

Insulators

are used in an electrical system to avoid unwanted flow of current to the earth from its supporting points. It is used to separate the line conductors from each other and from supporting structures. It has a high resistive path where no current can flow.

Insulating paper, cardboard, fiber glass

are used in transformers as insulating materials to separate the primary and secondary winding from each other and from the core. The most commonly used insulating material is transformer oil since it not only provides an insulating function, in addition, it also acts as liquid dielectric and coolant to the core of the transformer that is completely immersed in it. Hydrocarbon mineral oils are normally used as transformer oil.

Laminations

are used to reduce eddy current losses. Eddy currents are produced in a transformer core which distorts the main current and heats up the core that leads to losses. The area of a laminated core is smaller compared to a core that is only single piece. Having a smaller area means a higher resistance, thus, minimal current can flow and losses is reduced.

Tap changers

are used to regulate the output voltage of a transformer. It can be classified into two types: an on-load tap changer and an off-load tap changer. In an on-load tap changer, the tapping can be changed without isolating the transformer from the supply while in an off-load tap changer, the transformer needs to be disconnected before it is done.

core, the windings, the insulation, and its bushing.

essential parts of a PT are

Optical Potential Transformers

exploit the Faraday Effect, rotating polarized light in optical materials. These are used in optical equipment applications to measure resistances and reactance.

Epoxy

has a good thermal property and excellent adhesion but if not used properly during the manufacturing process, it can ruin components in a high voltage assembly. Thermal stresses during operation of the instrument can cause component damage due to uneven thermal expansion and contraction. In addition, the epoxy curing process may cause a large amount of heat and may damage parts due to heat generated during curing. Because the epoxy module can not be repaired, the assembly must be disposed of in the event of a failure. Another meaning is that failure analysis is severely limited and it is difficult to determine the problem.

Instantaneous Overcurrent Relays

have no deliberate time delay for operation. If the current inside the relay rises above the operating value, the relay contact closes immediately. The time interval between the pickup value and the closing contact of the relay is very small. The most important feature of the instantaneous overcurrent relay is the operating speed.

switchgear and control gear 2

is a collective term for electrical disconnect switches, fuses, and circuit breakers. It perform the functions of carrying, making and breaking the normal load current like a switch to control, protect and isolate electrical equipment. Switching and current interrupting devices play a significant role in the modern electrical network. The switching device here is called a circuit breaker

Lightning arrester

is a device used to protect equipment from damage from lightning strikes, such as power poles and towers, power transformers, circuit breakers, bus structures, and steel superstructures. It should have a rigid connection to ground on one side. The other side of the arrester is connected to a power line. Some lightning arresters are connected inside the switchgear or to the transformer .

Sulphur Hexafluoride

is a great insulator for high voltage applications since it is colorless, odorless, and non-toxic, liquified gas. It has an outstanding arc quenching properties and also allows for simplified design of switchgear because of size and weight reduction. However, with using SF6, the housing must be hermetically sealed to avoid inhalation since it is extremely hazardous if someone breathes in any SF6. This type of gas is denser than air which is why it settles in the bottom of one's lungs which may result suffocation. Also, poisonous gasses are formed whenever there are arcs.

Inverse-Time Overcurrent Relay

is a natural characteristic of all inductive rotating devices. The higher the input current, the faster the rotation of the rotating part of the device. The operating time varies depending on the input current. This natural characteristic of electromechanical inductive disc relays makes them well suited for overcurrent protection. If the error is serious, it clears the error faster. Time-domain characteristics are inherent in electromechanical induction disc relays, but with proper programming, the same characteristics can be achieved in microprocessor-based relays.

Electrical substation

is a part of the total electrical system (generation, transmission, and distribution) that transforms voltage from one level to another

overcurrent relay

is a relay that operates only when the value of the current is greater than the relay settling time It Protects the power system's equipment from fault currents.

high voltage bus

is a rigid conductor used to interconnect primary equipment. It is made out of extruded metal (such as aluminum pipe) and is supported by insulator posts. A high voltage bus must be mechanically braced to withstand mechanical forces caused by high fault currents

Capacitor banks

is a set of numerous identical capacitors which are either connected in series or parallel inside the enclosure and are utilized for the correction of power factor and protection in the circuit. Capacitors are devices used to provide reactive current to counteract inductive loads.

Overload overcurrent

is mainly an excess of current as compared to the rated load current. It is the condition wherein the current carried by the conductor or the equipment is already in excess of its rated ampacity.

Transformer turns ratio

is the quotient between high voltage / low voltage. It must match with protocol /nameplate values. In the power transformer with tap changer you will take advantage to make the register of each position from it giving extra information on its status and that of the On-Line Tap Changer (OLTC). This measurement will directly inform of the existence of shorts between turns

short-circuit

is the unintentional and electrical connection between two current carrying conductors of the circuit.

Ground fault

is the unintentional and electrically conducting connection between the ungrounded conductor and the ground, equipment grounding conductor, metallic equipment, or metallic raceways. It may only occur if the system is referenced to the ground.

Disconnect switch

is used to isolate parts of a substation during maintenance or repair periods. They can also be used to reconfigure connections between sub- transmission lines and/or power transformers. Disconnect switches are classified as either load break or no-load break. Load break switches can open and close with normal load current flowing through them. No-load break switches can only open and close if there is no current. Disconnect switches are not able to interrupt fault currents

Contact Resistance Test

is very important especially for circuit breakers, busbar and cable joints. this components carry large amount of current. As contact resistance increases the losses also increases, contact resistance test is used to detect and prevent future problems like, lower current carrying capacity and dangerous hot spots in the substation.

Air

it has the worst dielectric strength which will require distances to be the greatest for a given geometry and for the surfaces to be clean and free of dust over long periods of time to prevent arcing.

Overcurrent protective devices (OCPD)

protect systems against potentially hazardous effects of overcurrent which may either be an overload current or a short-circuit current.

Relays

senses faults and send signals or interruption message to trip in a specific point in the circuit. Protective relays provide an accurate and sensitive method of protecting electrical distribution equipment short circuits and other abnormal conditions.

Electromagnetic or Wound Type Conventional Potential Transformer

similar to the conventional oil filled wire wound transformers. They are used to up to 33kV voltage level application. It is very expensive because of the insulators.

Substation batteries

supplies power to operate devices such as protective relays, alarms, emergency lights, status indicators, communications equipment, and switchgear operating circuits. The size of the battery bank in the substation depends on the voltage required for operation of the DC circuit.

vacuum, oil, insulating gas, or air

the medium wherein the arc forms