A 75 HP, 3-phase, synchronous motor is connected to a 230-volt line. The motor is to be operated at 80% power factor. The motor nameplate lists a full load current of 185 amperes, a temperature rise of 40°C, and a code letter A. The conductors are to be made of copper and have type THHN insulation. The short-circuit protective device is to be an inverse time circuit breaker. Determine the conductor size, overload heater size, circuit breaker size, and the minimum size NEMA and IEC starters. The starter contains current transformers with a ratio of 300:5 to reduce current to the overload heater O Conductor size 250KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA5)(IEC R or S) Conductor size 250KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA6)(IEC R or S) Conductor size 350KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA5)(IEC R or S) Conductor size 300KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA5)(IEC R or S)

A 75 HP, 3-phase, synchronous motor is connected to a 230-volt line. The motor is to be operated at 80% power factor. The motor nameplate lists a full load current of 185 amperes, a temperature rise of 40°C, and a code letter A. The conductors are to be made of copper and have type THHN insulation. The short-circuit protective device is to be an inverse time circuit breaker. Determine the conductor size, overload heater size, circuit breaker size, and the minimum size NEMA and IEC starters. The starter contains current transformers with a ratio of 300:5 to reduce current to the overload heater O Conductor size 250KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA5)(IEC R or S) Conductor size 250KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA6)(IEC R or S) Conductor size 350KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA5)(IEC R or S) Conductor size 300KCMIL, Overload size X42 Inverse time circuit breaker 500A Starter size(NEMA5)(IEC R or S)

Electric Motor Control

10th Edition

ISBN:9781133702818

Author:Herman

Publisher:Herman

Chapter14: Phase Failure Relays

Section: Chapter Questions

Problem 1SQ: What is the purpose of phase failure relays?

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Concept explainers

Synchronous Motor

The synchronous motor is an AC electric type motor where at a steady-state the shaft rotation is synchronized with the supply current variable-frequency. To an integral number of AC cycles, the rotation period is exactly equal. The stator of the motor in the synchronous motor contains multi-phase AC electromagnets due to which a magnetic field is created that rotates in time with the oscillation of the line current. The rotor contains a permanent magnet and the rotor rotates in synchronization with the stator field at the same rate and provides the second synchronized magnetic field which is rotating in nature as a result. When the synchronous motor is supplied with independently excited multi-phase AC electromagnets on both the rotor and the stator, it is termed as a doubly-fed machine. The most widely used AC-type motors are the synchronous AC motor and the induction AC motors.

Question

9
A 75 HP, 3-phase, synchronous motor is
connected to a 230-volt line. The motor
is to be operated at 80% power factor. The
motor nameplate lists a full load current of
185 amperes, a temperature rise of 40°C, and
a code letter A. The conductors are to be
made of copper and have type THHN
insulation. The short-circuit protective
device is to be an inverse time circuit
breaker. Determine the conductor size,
overload heater size, circuit breaker size, and
the minimum size NEMA and IEC starters. The
starter contains current transformers with a
ratio of 300:5 to reduce current to the
overload heater
O Conductor size 250KCMIL, Overload size X42
Inverse time circuit breaker 500A Starter
size(NEMA5)(IEC R or S)
O Conductor size 250KCMIL, Overload size X42
Inverse time circuit breaker 500A Starter
size(NEMA6)(IEC R or S)
O Conductor size 350KCMIL, Overload size X42
Inverse time circuit breaker 500A Starter
size(NEMA5)(IEC R or S)
O Conductor size 300KCMIL, Overload size X42
Inverse time circuit breaker 500A Starter
size(NEMA5)(IEC R or S)
+

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