EMR-5000
IM02602012E
87M - Motor Differential Protection
Available Elements:
87M[1] ,87M[2]
Functional Description
The motor differential protective element of the device uses a flux summing, self balancing method of motor differential
protection. This is achieved by summing the current entering into a motor winding with the current exiting the same
motor winding. This is a very accurate and reliable method of differential protection, as there is no need to compensate
for differences in sensor inaccuracies, or mismatches between current sensors, that may result in a difference current.
The conductor feeding the motor winding is passed first through a differential current sensor and then to the motor
winding. The output of the winding is then brought back through the sensor.
The current flowing out of the winding should always be equal to the current flowing into the winding under normal
operating conditions. The flux resulting from the current flowing through the input and output conductors is summed
within the differential current sensor. The output of the sensing transformer is the vector sum of the two equally
opposing currents in the two conductors. Typical, a differential sensor would have a turns ratio of 50:5. This method of
detection provides both Phase-to-Phase fault detection as well as Phase-to-Ground protection.
To set the parameter for this element, enter [
Protection Para/Set [x]/I-Prot]
. Here you will find the 87M elements.
www.eaton.com
535
1
X3.
2
3
4
5
6
7
8
9
10
11
12
IA
1A
5A
N
IB
1A
5A
N
IC
1A
5A
N
IX
1A
5A
N
M
C
A
B
1
X4.
2
3
4
5
6
7
8
9
10
11
12
IA
1A
5A
N
IB
1A
5A
N
IC
1A
5A
N
IX
1A
5A
N
Do not use
