Reduced Voltage Starting 370
This class describes the various methods of reduced voltage starting and explains when each type of starter is used.
Number of Lessons 14
- What Is Reduced Voltage Starting?
- Across-the-Line Starting
- Reasons for Reduced Voltage Starting
- RVS in DC Motors
- RVS in AC Motors
- Primary Resistor Starting
- Autotransformer Starting
- Wye-Delta Starting
- Part Winding Starting
- Solid-State Starting
- Choosing an RVS Method
- Define reduced voltage starting.
- Describe across-the-line starting.
- Explain why reduced voltage starting is necessary.
- Describe reduced voltage starters in DC motors.
- Identify various types of AC motor reduced voltage starters.
- Describe primary resistor starting.
- Describe autotransformer starting.
- Describe wye-delta starting.
- Describe part winding starting.
- Describe solid state starting.
- Describe factors used to select a reduced voltage starter.
- Describe common troubleshooting techniques.
across the line
Connected directly to the power lines, allowing full voltage when the motor starts.
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.
An electrical terminal that usually carries a positive electrical charge. An anode serves as the output terminal in an SCR.
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.
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.
An electrical terminal that usually carries a negative charge. A cathode is common to both the input and output terminals in an SCR.
A term commonly used for an autotransformer starter. A compensator raises current levels to compensate for the reduced voltage.
The voltage induced in the armature of a DC motor that opposes the applied voltage and limits armature current.
The control terminal in a silicon controlled rectifier. The gate is the input switch that opens or closes the circuit.
The building where the utility company houses large linked AC generators to create the massive power for widespread use.
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.
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.
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.
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.
The National Electrical Code table that shows kilovolt amps per horsepower with lock rotor for motors.
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.
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.
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.
The reduction in voltage level from the source to the load caused by conductor resistance.
A type of reduced voltage starter that makes use of the characteristics of wye and delta connections to reduce voltage without lowering current.
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.