1. LOW VOLTAGE MCC – STUDY REPORT ON UNWANTED BREAKER
OFF PROBLEM DURING EXTERNAL FAULTS
LOCATION : RO PLANT KHORFAKKAN
EQUIPMENT DETALIS : RO PLANT MCC & SEA WATER MCC
Report Prepared By:
Mr.Rajendrakumar.A.P
Electrical Supervisor
SEWA RO plant Khorfakkan

2. THE PROBLEMAND ITS HISTORY
Since the beginning of the plant in 2009, it has been observed that during any external faults
i.e., faults in distribution network in khorfakkan RO plant MCC as well as Sea Water intake MCC
incomer breakers are getting off and the system shows no indication of faults. The faults in the
distribution networks are quite common especially during summer due to cable faults, which results
in unwanted tripping of the RO trains.
PRELIMINARY OBSERVATIONS
When referred to the drawing (figure No.1Breaker open control circuit) I concluded the possibilities
to the following two points.
1. OFF command from DCS
2. Breaker opens through under/over voltage relay contact(12UVR1)
The first point was ruled out when checked the DCS history. In the DCS history there was
no OFF command to the breakers. The second point needed to be confirmed. The settings of the
relay (time delay) found to be disturbed and were in the higher side. On delay found as high as 10
sec and it was reduced to 5 sec. So, with the permission of Plant Manager the breaker opening
contact of the under/over voltage relay kept open in the sea water intake incomer # 2 which is
having relatively un important loads(up-stream system gives back up protection for the same).
During another external fault it was found that sea water incomer breaker #2 remained ON and all
other three breakers got OFF. Further it was decided to keep sea water incomer breaker # 1 OFF
contact from the under/over voltage relay to keep open. During the next external faults sea water
incomer breakers did not get OFF. So it was almost confirmed that the problem is resulted from the
under/over voltage relay.
FIGURE 1: BREAKER OPEN CONTROL CIRUIT FIGURE 2: UNDER/OVER VOLTAGE RELAY
Then a genuine question arised, how four relays can malfunction simultaneously or behave
similar to a fault. The chance of all relays getting faulty at the same time is a remote possibility, so
it was necessary to find out the root cause. Downloaded the relay manual from internet and studied.
The following points about the relay characteristic found worth noting.
1. DRV3 is immune to voltage dips < 40 ms.

3. 2. When the voltage is < 0.7 Ue for a time longer than 60 ms, the output relay de-energizes
instantaneously.
CONCLUSION
A fault can result in the second condition and instantaneously de-energise the output relay of the
under/over voltage relay resulting in opening of the breaker.
SOLUTION
Introducing a timer relay in the control circuit will be a cost effective and permanent solution to the
problem. The modified circuit diagram is shown .Figure.3.
The required timer delay details:
On Delay timer
Input: 110 V DC (if universal 24 to 240 Volt AC/DC)
Time Range: 1 to 10 sec (0.5to 10 sec)
Aux Contacts: 1 NO & 1 NC.
Compact DIN rail mount, SPDT
Submitting for necessary approval for successful implementation.

4. Below given isa content from given web address which shows study of similar problem but the report is
not accessible to non members or need to be paid.
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5638901&filter%3DAND%28p_IS_Number%3A56
38851%29
Currently, under-voltage trip devices are widely installed in circuit breakers of low-voltage distribution networks and
end users' sides. These protection devices can prevent equipments from damage when voltage sag or power
supply interruption occurs. Although relay protection devices can act correctly and clear the fault as soon as
possible when a ground or inter phase fault occurs in the nearby high-voltage transmission network, instantaneous
action of under-voltage trip devices may lead to widespread loss of load, fluctuation of frequency, even worse,
cascading failure and collapse of the power system. The widespread load loss accidents arising from under-
voltage trip devices happened in recent years are summarized in this paper. Two typical load loss accidents
happened in Beijiao substation are introduced. The effects of under-voltage trip devices on power system are
discussed base on EMS accident recall, PMU, fault recorder and other tools. Finally, suggestions on management
of under-voltage trip devices and accident precautions are proposed.
-THANKS –