IMM 8001/8002 – Digital Motor Protection Relay
ICE / CEE
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IMU307-1 GB Ind. B
15
If the definite time operating level Io>> is in service, the use of a steadying resistor as defined below
is recommended.
The inaccuracy of the CTs measurement during the starting or re-acceleration periods
may result in unexpected protection trips. To solve these problems, it is highly
recommended to use a stabilising resistor connected in series with the relay earth fault
input.
Simplified formula to calculate ohmic value :
Rst
= [
>>
>
Io
Ist
x
INTc
x
RTC
] – RTC – R relay
with :
Rst
= calculated stabilising resistance, in Ohm
RTC
= line CTs secondary resistance, in Ohm
INTc
= CTs rated value, in A
Ist>
= starting current, in multiples of In
Io>>
= earth fault protection operating level, in A
R relay = relay input resistance: 0.2 Ohm
Type of resistor to be used :
High power adjustable wire-wound resistor with a rheostat-type connection :
0 - 5 Ohms 240 W for secondary CTs with IN = 5A
0 - 20 Ohms 240 W for secondary CTs with IN = 1A
Choose the suitable earth fault input of the relay depending on the secondary nominal value of the
protection CTs. The relay has 1A earth fault input and 5A input (see chapter 3.2.).
Connection to ring CT
Connection to a ring CT is done on the ring CT input, terminals 14 and 16, which is the same as the
residual connection 1A input.
The relay can operate with a CEE 100-turn ring CT
(see mechanical characteristics in
drawing No 142941
) :
- closed 100-turn ring CT for indoor use, type TF 50-1, TF 80-1, TF 145-1, TF 198-1, TF
245-1
- closed 100-turn ring CT for outdoor use, type TFE 40-1
- split 100-turn ring CT for indoor use, type TO 105-1