Reduced Voltage Starting 370

across the line

Connected directly to the power lines, allowing full voltage when the motor starts.

across-the-line starting

A method of motor starting that applies full line voltage to the motor. In this start, the motor is connected directly to the power source.

anode

An electrical terminal that usually carries a positive electrical charge. An anode serves as the output terminal in an SCR.

autotransformer starter

A type of reduced voltage starter that uses an autotransformer to allow voltage levels to be reduced to 80, 65, and 50% of full line voltage. Also commonly called a compensator.

autotransformer starting

A method of reduced voltage starting that uses a tapped autotransfomer to reduce voltage levels to either 80, 65, or 50% of full line voltage.

cathode

An electrical terminal that usually carries a negative charge. A cathode is common to both the input and output terminals in an SCR.

compensator

A term commonly used for an autotransformer starter. A compensator raises current levels to compensate for the reduced voltage.

counter emf

The voltage induced in the armature of a DC motor that opposes the applied voltage and limits armature current.

gate

The control terminal in a silicon controlled rectifier. The gate is the input switch that opens or closes the circuit.

generating station

The building where the utility company houses large linked AC generators to create the massive power for widespread use.

inrush current

The initial surge of current into the windings. Inrush current can be up to ten times higher than the continuously needed current because there is low initial resistance.

National Electrical Code

The standard for minimum safe electrical installations. The National Electrical Code is adopted in some form as law in all 50 states.

open transition

A type of motor circuit that needs to momentarily open the circuit before applying full voltage to the motor. Open transition circuits are cheaper to use but can cause a current surge when reconnected.

overload protection

The use of devices such as overload relays to open the circuit in the event of an overload to prevent the motor from overheating.

part winding motor

A type of motor that has two separate sets of primary windings. Part winding motors first energize only half of the windings, then the other half as the motor comes up to speed.

part winding starter

A type of reduced voltage starter that applies power to only one set of windings, then to the other set as the motor comes up to speed.

part winding starting

A method of reduced voltage starting that applies power to only one set of windings, then to the other set as the motor comes up to speed.

power distribution system

A circuit that travels from generating stations to end users to provide electrical power.

primary resistor starter

A type of reduced voltage starter that uses resistors to create an initial 30% drop in voltage before allowing full current to the motor.

primary resistor starting

A method of reduced voltage starting that connects resistors in series with the motor to produce an initial 30% voltage drop before allowing full current to the motor.

reduced voltage starter

A category of motor starters that reduce the power coming into the motor when it is initially started.

rheostat

A type of variable resistor that is used to resist electric current. A rheostat is used in DC motor reduced voltage starters.

silicon controlled rectifier

A digital switch used to quickly control heavy currents. SCRs are used in solid state reduced voltage starters.

solid state starter

A type of reduced voltage starter that uses an SCR to control current levels at startup. Solid state starters have no moving parts, so they are very durable.

solid state starting

A method of reduced voltage starting that uses an SCR to control current levels at startup. This method is expensive, but offers variable voltage and torque.

squirrel cage induction motor

A type of three phase AC motor whose rotor is constructed by connecting metal bars together at each end. It is the most common AC motor type.

Table 430.7(B)

The National Electrical Code table that shows kilovolt amps per horsepower with lock rotor for motors.

tap

A wire connected to a specific point on a transformer's secondary winding. This allows the autotransformer to use different turns ratios to vary voltage.

turns ratio

A comparison of the number of turns in the primary versus the number of turns in the secondary. Autotransformers step voltage up or down based on the turns ratio.

two-point acceleration

Having one resistor in series with the motor to provide a smooth start. Adding additional resistors adds additional points of acceleration for an even smoother start.

voltage drop

The reduction in voltage level from the source to the load caused by conductor resistance.

wye-delta starter

A type of reduced voltage starter that makes use of the characteristics of wye and delta connections to reduce voltage without lowering current.

wye-delta starting

A method of reduced voltage starting that first connects a motor in a wye to reduce voltage, then reconnects the motor in a delta to provide full line voltage.