Motor Protection Requirements; Features; Introduction 1.1 Motor Protection Requirements - GE 269Plus Instruction Manual

1 INTRODUCTION

MOTOR PROTECTION REQUIREMENTS

269 PLUS INSTRUCTION MANUAL 1 INTRODUCTION 1.1 MOTOR PROTECTION REQUIREMENTS
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Three phase AC motors have become standard in modern industry. These motors are generally rugged and
very reliable when used within their rated limits. Newer motors, however, tend to be designed to run much
closer to these operational limits and thus there is less margin available for any type of abnormal supply, load,
or operating conditions.
A modern protective device is required to fully protect these motors. Accurate stator and rotor thermal model-
ing is necessary to allow the motor to operate within its thermal limits and still give the maximum desired out-
put. As well, other features can be incorporated into a modern relay to fully protect the motor, the associated
mechanical system, and the motor operator from all types of faults or overloads.
Motor thermal limits can be exceeded due to increased current from mechanical overloads or supply unbal-
ance. Unbalance can greatly increase heating in the rotor because of the large negative-sequence current
components present during even small voltage unbalances. A locked or stalled rotor can cause severe heating
due to the associated large currents drawn from the supply. Many motor starts over a short period of time can
cause overheating as well. Phase-to-phase and phase-to-ground faults can also cause damage to motors and
hazards to personnel. Bearing overheating and loss of load can cause damage to the mechanical load being
driven by the motor.
The ideal motor protection relay should monitor the rotor and stator winding temperatures exactly and shut off
the motor when thermal limits are reached. This relay should have an exact knowledge of the temperature and
proper operating characteristics of the motor and should shut down the motor on the occurrence of any poten-
tially damaging or hazardous condition.
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The 269Plus Motor Management Relay uses motor phase current readings combined with stator RTD tem-
perature readings to thermally model the motor being protected. In addition, the 269Plus takes into account the
heating effects of negative sequence currents in the rotor and calculates the cooling times of the motor. The
relay also monitors the motor and mechanical load for faults and problems. With the addition of a GE Power
Management Motor Protection Meter (MPM), the 269Plus may also monitor voltages and power and perform
several protection functions based on these values.

1.2 FEATURES

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The GE Power Management model 269Plus Motor Management Relay is a modern microcomputer-based
product designed to provide complete, accurate protection for industrial motors and their associated mechani-
cal systems. The 269Plus offers a wide range of protection, monitoring, and diagnostic features in a single,
integrated package. All of the relay setpoints may be programmed in the field using a simple 12-position key-
pad and 48-character alphanumeric display. A built-in "HELP" function can instruct the user on the proper func-
tion of each of the programming keys and on the meaning of each displayed message.
One 269Plus relay is required per motor. Phase and ground fault currents are monitored through current trans-
formers so that motors of any line voltage can be protected. The relay is used as a pilot device to cause a con-
tactor or breaker to open under fault conditions; that is, it does not carry the primary motor current.
The 269Plus incorporates the following features: custom curve selectability, motor statistical records, speed
switch input, differential relay input, 10 RTD inputs, single-shot emergency restart feature, an RS485 communi-
cations port, unbalance input to thermal memory, start inhibit feature, and spare input.
The 269Plus custom curve feature provides additional flexibility. If one of the eight standard overload curves is
not suitable for the application under consideration, the user can enter their own breakpoints to form a custom
curve. As such, the 269Plus can offer optimum motor protection in situations where other relays cannot. Such
applications include induced fan drives where the motor stator and rotor thermal capacities can differ signifi-
cantly.
GE Power Management 269Plus Motor Management Relay 1-
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