Motor Control, LVL 2. Lesson 6: Special Purpose Starters

Wye-delta starters

? are best suited for applications where low starting torque and minimal line current are required.

Autotransformer starters

? are constructed with two or three wye-connected single-winding autotransformers connected to timer-controlled contactors.

Autotransformer starters

? are one of the best options when maximum starting torque and minimum starting current are required for a particular application.

Wye-delta starters

? are one of the least expensive options for large horsepower motors.

Soft-start starter

? controllers are commonly used in applications requiring smooth starting and stopping of motors and driven machinery.

Soft-start starter

? controllers are electronic devices that offer greater control during the starting and stopping of a motor.

Soft-start starter

? controllers offer adjustable ramp-up time by gradually increasing the voltage and current supplied to the motor and ramp-down control that reduces motor voltage and current for deceleration.

Electrical

? interlocks operate through auxiliary contacts on the contactors that disable the coil of a second contactor when the first contactor is closed or disable the first contactor when the second contactor is closed.

Mechanical

? interlocks prevent both the forward and the reverse contactors from closing at the same time using a cam to prevent the simultaneous closing of the two armatures.

Primary resistor starting

? is a reduced voltage starting technique that connects a resistor in series with each phase supplying the motor.

Autotransformer starting

? is one of the most efficient and effective reduced voltage starting techniques.

Autotransformer starters

? offer more reduction of line current than any other reduced voltage starting method.

Solid-state reduced voltage starters

? provide the smoothest acceleration and greatest control of current and torque for squirrel cage motors than any other starting technique.

Part-winding starting

? requires no special equipment and is inexpensive to purchase, install, and maintain.

Reversing

? starters are used in industrial processes that require the motor to run both forward and backward.

False

A forward/reverse starter requires two overload relay assemblies.

dual voltage

A part-winding starter is only used with a ? motor capable of part-winding starting.

2

A part-winding starter requires ? motor starter(s) and one timing relay.

Wye-delta starting

A special six-lead or twelve-lead motor that can be connected in either a wye or delta configuration must be used in which type of starting method?

SCR

A(n) ? is composed of a cathode, anode, and gate.

Pushbutton Interlocking

Although the combination of mechanical and electrical interlocks provides a high level of protection in reversing circuits, ? is sometimes used when an additional form of interlocking is required.

Squirrel cage

Autotransformer starters are best suited for what types of motors?

Low / higher

Autotransformer starters function by maintaining a relatively ? primary current, but allows a ? secondary current to start the motor.

Solid-state reduced voltage starting

By triggering the SCR on and off at specific intervals during each cycle of the sine wave, this starting method controls the voltage and current delivered to the motor windings while the motor is accelerating.

open transition

Cost and ? conditions are the two biggest disadvantages of an autotransformer starter with an autotransformer in each leg of the 3-phase supply.

II. Part-winding starting VI. Wye-delta starting

Current reductions are achieved by temporarily modifying the wiring configurations to the motor in which types of starting?

Part-winding starting

Full voltage is applied to the motor at all times through acceleration and up to normal speed in what type of starting method?

primary resistor starting

Heat is the biggest disadvantage of ? .

False

If faster acceleration is required, additional resistors should be added in parallel to the existing resistors and controlled by additional timers and contactors to a primary resistor starter.

Solid-state reduced voltage starting

In ? , a silicon-controlled rectifier (SCR) controls the voltage and current to the motor during acceleration.

autotransformer starter

In applications that require frequent starting or long acceleration periods, a(n) ? would work very well.

Control Power

In troubleshooting a control circuit, the first step is to verify that ? are (is) present.

False

Most power distribution systems are designed for huge current fluctuations on their power grid.

False

Motor feed conductors can be sized based upon current measurements made in the field.

True

Part-winding starting is not suitable for long startup times or high inertia loads.

lowers / lessens

Reduced voltage starting ? inrush currents and ? the impact on the distribution systems.

False

Reduced voltage starting techniques for DC motors have replaced DC motor drives in many DC motor applications.

True

Reversing motor starters are normally factory wired for electrical interlocking.

2/1

Reversing starters consist of ? contactor(s) and ? overload relay assembly (assemblies).

lower

Since part-winding starters are connected to only one set of coils at startup and both sets of coils in parallel when the motor is up to speed, the motor must operate at the ? voltage reading.

Full Voltage

Smaller 3-phase motors are normally controlled using ? across the line starters.

True

Swapping any two power phase leads will reverse the direction of a three-phase motor.

Longer/Longer

The ? the gate has a signal, the ? the SCR remains on, and the greater the voltage and current is supplied to the motor.

Primary resistor starting

The addition of resistance in series with each phase produces a voltage drop across the resistor, resulting in a reduced voltage and current to the motor while starting. Once the motor accelerates to the proper speed, a contactor controlled by a timer closes contacts that are wired in parallel with the resistors, effectively shunting the resistors in each phase and connecting the motor directly to full line voltage.This explains what starter operation?

Open/Closed

The basic wye-delta starter configuration is designed for ? transition starting, although ? transition starters are available at an extra cost.

series /parallel

The coils of a dual voltage motor are connected in ? for higher voltage and in ? for lower voltage.

Mechanical Interlocks

The dotted lines in the diagram identify ?

True

The high inrush currents for large horsepower AC motors can cause interference on the power distribution system.

L1 (phase A) and L3 (phase C)

The industry standard for reversing a three-phase motor is to switch which two power leads?

True

The two motor starters of a part winding starter can be sized for one-half of the FLC of the motor since neither starter will conduct more than one-half of the motor current except at startup.

2

The windings of dual voltage motors have ? set(s) of coils in each winding.

50% / 65% / 80%

The windings of the autotransformers are typically tapped at ? , ? , or ? of the line voltage.

Start/Run

The wye winding is used in the ? configuration, and the delta winding is used in the ? configuration.

Ladder Diagram

Troubleshooting control circuits involves using a ? to analyze the control logic.

primary resistor starters

Typically, ? drop the voltage and current values to approximately 80% of the normal line readings.

Part-winding starting

What motor starting technique applies power to part of the motor windings at startup and then connects the remaining coils for normal speed?

Gate

When a signal is applied to the ? , it acts as a "trigger" that turns the SCR on and off.

primary resistor starting

When applications require modest reductions in line current and torque while providing smooth acceleration, ? would be best suited.

primary resistor starting

When operations require a slow and constant start, ? should be used.

Equal to

When troubleshooting reduced voltage starters, the voltage during the running stage should be ? the line voltage.

Closed transition

Which type of autotransformer starter only has autotransformers in two legs of the three-phase supply?