269 Plus Motor Protection System

Protection and Control

The 269 Plus is a digital relay designed to

provide complete and accurate protection

for industrial motors and their associated

mechanical systems. Protection functions

include:

Start and Running

The motor is protected under both

acceleration and running conditions.

An alarm or trip may occur based

on acceleration time, the number of

starts per hour, the time b e twe e n

s t a r t s , o r mo t o r o v e r l o a d

conditions.

Overload

One of eight standard overload curves may

be programmed based on manufacturer’s

locked rotor t ime capabi l i ty.

Alternatively the user may program a

custom curve using the built-in FlexCurve™

function. The motor’s service factor value

is entered as the overload pickup level.

FlexCurve™

A smooth custom overload curve is created

within a selected range using FlexCurve™.

This curve can be used to protect motors

with different rotor damage and stator

damage curves, allowing total motor

design capacity with complete protection.

Unbalance (Negative Sequence)

Unbalanced supply voltages means a large

increase in the negative sequence current

which can result in greatly increased rotor

heating. The relay uses the ratio of the

negative to positive sequence currents to

bias the thermal model. Unbalance and

phase loss protection is also provided.

Undercurrent (Minimum Load)

The undercurrent function is used to detect

a decrease in motor current caused by a

decrease in motor load. This is especially

useful for indication of conditions such as

loss of suction for pumps, loss of airflow

for fans, or a broken belt for conveyors. A

separate undercurrent alarm level may be

set to provide early warning.

Ground Fault

For zero sequence ground fault protection,

all three of the motor conductors must

pass through a separate ground fault CT.

CTs may be selected to detect either high

impedance zero sequence ground faults

or residual ground faults. The trip can be

instantaneous or time delayed by up to 20

seconds. A low level of ground fault pickup

is desirable for maximum stator winding

protection. A 50:0.025 A CT or 5 A CT may

be used for ground fault detection.

Rapid Trip/Mechanical Jam

Quick motor shut down can reduce

damage to gears, bearings, and other

mechanical parts associated with the drive

combination. A current surge will cause the

relay assigned to the rapid trip/mechanical

Stator Overtemperature

Overtemperature protection of the stator

windings is provided by monitoring up to

six stator RTDs. If less than six RTDs are

used for stator monitoring, the remaining

RTDs may be used for any other temperature

monitoring function desired. Individual RTD

alarm, high alarm and trip levels are set by

the user.

Temperature Monitor

A total of 10 RTD inputs are available. Any

RTD inputs not used for stator RTD protection

can be used for other temperature

monitoring functions. Separate alarm and

trip level temperatures can be selected for

each RTD.

MotorMatch

To obtain maximum use from the protected

motor, the MotorMatch system modifies

the initial relay parameters to match actual

measured motor characteristics. The key

elements include:

n Accumulated I2t in the memory

n RTD input to the memory

n Learned cooldown time from run to stop

n Learned cooldown time from run-overload

to run-normal

n Learned acceleration time

To learn the cooldown time, the 269

Plus tracks the stator RTD temperature

and calculates the rate of cooling. If an

ambient air RTD is also used, the relay uses

this value in its calculation.

The learned accelerating I2t value is

obtained by measuring actual inrush

currents and acceleration time. This

learned value is only accepted after

sufficient starts have been sampled.

Start Inhibit with Auto-Timed

Lock-Out

MotorMatch provides the 269 Plus with the

true motor thermal capacity. When the

Start Inhibit feature is enabled, the thermal

memory has to sufficiently discharge to

make the start possible. The 269 Plus uses

the “learned start capacity required” to

determine if sufficient thermal capacity

is available for a start. The start inhibit

lock-out time is automatically adjusted to

allow for optimum motor usage.

Emergency Restart

It may be necessary to restart a faulted

motor for reasons of production or safety.

To override a start inhibit or overload trip

lockout condition, the emergency restart

feature can be used. This clears the

thermal memory, allowing a manual reset

and restart.

The 269 Plus can be programmed to

provide a single shot emergency restart

following an overload trip. The accumulated

I2t value is automatically reduced to a level

that would allow a restart. After the restart

attempt, if the relay trips the motor again

on running overload, it will remain latched

for the appropriate lock-out time.

Thermal Modeling

A unique feature of the 269 Plus relay is

its ability to compute the motor I2t value

based on actual motor load current. The

thermal model calculates this value in

terms of thermal capacity used. The RTDs

measuring the stator temperature act as

a thermal capacity check to confirm the

value calculated by the thermal model. The

thermal capacity used is then updated to

reflect the higher of the two values. This

accounts for heat due to I2t as well as

motor heating due to loss of cooling or

Exponential Cooldown

The 269 Plus has a true exponential

cooldown characteristic which mimics

actual motor cooling rates. This allows

motors to be load cycled more frequently

since the initial rate of cooling is very

steep. Two setpoints are required to use

the exponential cooldown, the full load

current (FLC) reduction and the running

cool time.

The FLC reduction is the amount of thermal

capacity used when the motor is running

at a constant 100% FLC condition. This

represents the constant percentage

difference between the cold damage curve

and the hot damage curve. The running

cool time is the time for the thermal

memory to discharge from 100% to 0%

with the motor running in a non-overload

condition. If the motor comes from an

overloaded condition to a light load

condition, then the cooling rate is much

faster initially and the thermal capacity

used would be reduced accordingly.