Transformers

What is a phase?

A single electrical circuit.

Anything above 600 volts is _____?

HIGH VOLTAGE

The winding to which the load is connected is called the _____ winding.

SECONDARY

What is magnetic flux?

The total numbre of lines or force issuing from a pole. (north or south)

What does grounded mean?

(Earthed) Connected to earth or to some conducting body which serves in place of the earth.

The capacity of a transformer is rated in ____ _____.

KILOVOLT - AMPERES (kVA).

In a transformer the _____ current will always flow in such a direction that its magnetizing action will oppose the magnetizing action of the primary winding.

SECONDARY

If the transformer is used as a _____ transformer, the low voltage winding is the primary.

STEP-UP

What does 'ratio of a transformer" mean?

The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.

What does "rating" mean?

A designated limit of operating characteristics based on definite conditions.

What is an Electromagnet?

A magnet made by winding a coil of wire around a soft iron core. Current passed through this winding produces magnetic lines of force in the coil.

What is a fuse?

A part of a circuit made of a low melting point material so that it will melt and break the circuit when a specified current exceeded. Always the weakest point in the circuit.

What is a fault?

A partial or total local failure in the insulation or continuity of a conductor.

What is a rotation meter?

A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.

What is a transformer?

A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.

What is a grounded system?

A system of conductors in which at least one conductors or point (usually the middle wire or neutral point of a transformer or generator windings) is intentionally grounded either solididly or through a current-limiting device.

What is a wigginton?

A test instrument used to indicate low voltage potentials in the range of 110 to 600 volts either alternating or direct current. (slang term: wiggy)

What is a step down transformer?

A transformer in which the primary is the high voltage winding and the secondary is the low voltage winding.

What is a step up transformer?

A transformer in which the primary is the low voltage winding and the secondary is the high voltage winding.

What is a distribution transformer?

A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.

What are constant current transfomers?

A transformer which when supplied from a constant potential source automatically maintans a constant current in its secondary circuit under varying conditions of load impedance. Used on series street light circuits.

A transformer that has its primary and secondary windings electrically connected is called an _____.

AUTOTRANSFORMER

A variable transformer is a continuously adjustable _____.

AUTOTRANSFORMER

The _____ has the primary winding and secondary winding electrically connected.

AUTOTRANSFORMER

What is a short circuit?

An abnormal connection of relative low resistance, whether made accidentally or intentionally, between two point of different potential in a circuit.

What is an ammeter?

An instrument used to measure electrical current.

Transformer losses are classified as _____ and _____.

COPPER LOSSES; CORE LOSSES

Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.

CORE: Core losses are caused by eddy currents set up by the magnetic field.

The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.

CURRENT

_____ currents are reduced by laminating the core.

EDDY

A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.

ELECTROMAGNETIC INDUCTION.

When an alternating current is applied to the high-voltage (H) winding of a transformer with no load on the secondary (X) winding, a small current, called the _____ current, flows in the primary.

EXCITING

With no load on the secondary winding, a small current flows in the primary called _____ _____.

EXCITING CURRENT.

Core losses are _____ loss and _____ - _____ loss.

HYSTERESIS; EDDY-CURRENT

What does polarity refer to?

It refers to the direction of current flow in a closed circuit.

The output or capacity of a transformer is rated in _____ - _____.

KILOVOLT - AMPERES (kVA)

Autotransformers are not safe when they supply a _____ voltage from a high voltage source.

LOW

Instrument transformers reduce high voltages and currents to safe, usable values for the operation of _____ equipment.

MEASURING

Instrument transformers reduce high voltages and currents to safe, usable values for the operation of _____ _____.

MEASURING EQUIPMENT

The transformer winding to which voltage is supplied is called the _____ winding.

PRIMARY

The winding to which voltage is supplied is called the _____ winding.

PRIMARY

What is leg(s)?

Reference to a jumper or conductor, to or from a piece of electrical equipment.

The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.

SAME

To minimize flux leakage in transformer construction, the primary and secondary windings are placed on the _____ leg(s) of the core.

SAME

The transformer winding to which the load is connected is called the _____ winding.

SECONDARY

To prevent injury to personnel when servicing any equipment connected to a current transformer, the secondary winding must be ____ - _____.

SHORT CIRCUITED: Unless the secondary winding is short-circuited, a high open circuit voltage that can be dangerous will exist.

If the transformer is used as a _____ transformer, the high voltage winding is the primary.

STEP-DOWN

Two coils wound on a closed iron core form a simple _____.

TRANSFORMER

What is Hysteresis?

The loss of power required to reverse the core magnatism each time the current reverses. This loss is caused by friction between the molecules of iron as these particles are aligned first in one direction and the in the opposite direct as current direction reverses.

What is a flux?

The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.

What does "rated KVA of a transformer" mean?

The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.

What does transformer efficiency mean?

The ratio of useful power output to its total power input.

What is primary winding?

The winding of a transformer to which electrical energy is supplied.

What are class 400 transformers?

Transformers designed for 4800 volt primary operation, but the secondaries are connected 240/480 volts. Winding ratio is 10:1

What are class 200 transformers?

Transformers with 4800 volt primaries and 120/240 volt secondaries, either pole or subway type, with two secondary windings terminating at internal links which provide for parallel operation of the secondary windings at 120 volts or series operation at 120/240 volts. Winding ration in series is 20:1

A magnetic field changing with respect to the conductor will generate a _____ in the conductor.

VOLTAGE

The energy is always transferred without a change in frequency, but usually with changes in _____ and _____.

VOLTAGE; CURRENT