test 6 Flashcards
excess energy redirected back to AC supply
Regenerative brake
The Frequent starting and stopping of a motor for short periods of time
jogging
the arrangement of contacts is such a way that both sets of contacts cannot be physically closed at the same time
mechanically interlock
motor breaking in which motor connection is reversed so that the motor develops a counter torque the acts as a brake
plugging
a relay that has an infinite number of possible output voltages within the rated range of the relay
analog - switching relay
Used to reduce the time it takes a rotating motor to stop spinning
braking
The frequency of the voltage used to control motor speed
fundamental frequency
the trip point from the time the motor starts until the first time the overloads trip
cold trip
a stopping method in which the level of voltage applied to motor is reduced as the motor decelerates
Ramp stop
The part of the relay to which the control component is connected
input circuit
a converter is a device that converts ______ to ________
AC voltage to DC voltage
although any 2 lines may be interchanged to reverse a 3 phase motor, the industry standard is to interchange ___ and ____.
L1 and L3
reversal of a DC compound motor is accomplished by reversing the _________ connection only
armature windings
What is ramping
acceleration or deceleration of a motor over some period of time
A limitation of EMRs is they
generate EMI on power lines
Current to an AC motor drive is limited by
the size of the conductors to the drive
OCPD size
transformers delivering power to the system
The advantage of using friction brakes is
Simplified maintenance and lower initial cost
AN inverter is a device that converts _____ to _____
DC voltage to AC voltage
AC motors should not be driven at speeds greater than ___ above their rated nameplate speed.
10%
A ________ is an SSR that turns on a load when the voltage at the load crosses near or at the zero point
Zero - switching relay
to prevent damage to diodes in a converter and to AC motor drive electronic circuits protection against ______ must be included in the drive.
Transient voltages
What are the 2 physical qualities which must be connected in a motor drive?
speed and torque
a variable frequency drive provides 48 hz AC voltage to a 3 phase 480 volt AC motor which has 6 poles per phase. What would be the synchronous speed of the motor with the voltage applied.
(120*f)/#of poles
(120*48)/6
960
5 limitations for a SSR
- requirement for a heat sink due to voltage drop across the switch
- residual resistance
- 1 set of contacts
- current leakage
- complete device needs to be replaced
what are the 3 main sections of an AC motor drive
Converter
DC bus
inverter
name the parts of a solid state relay
input circuit optocoupler LED output circuit photo detector light
