Emergency lube oil pump

A

Thread Starter

amin

in emergency lube oil pump driving should we consider a normally close contactor or fail safe contactor?
 
>in emergency lube oil pump driving
>should we consider a normally close
>contactor or fail safe contactor?

No need in my opinion. Emergency lube oil pump should be supplied by dc power as well as your control system. The dc power should be uninterruptable in any condition not like ac power (unless you are equipped with UPS). As long as the dc power system is maintained correctly, there is no worry about Emergency pump control. It will always work when it should. So normally open contactor should suffice in any condition.

The things you should consider is removing or bypassing the overload of emergency pump. The emergency pump motor usually equipped with overload and if it was not set correctly, it will disturb the operation of emergency pump which is very dangerous. I bypassed the overload protection of emergency lube oil pump. The emergency pump must always work when it needed. emergency pump supplies the lube oil to the bearing when main pump and ac pump had failed. So emergency pump must not fail in this condition. It can die for greater purpose. It is our last defense. So by simply bypass the overload I feel safer now.
 
Wiring should be failsafe as much as possible. The 3 field cables to the motor in our site is via normally closed contactors. The contactors used to bypass the current limiting resistors are normally open. Hence a failure of control supply will cause the motor to run at designed current/voltage/speed.

From a control wiring it's easiest to think of having to turn the pump off with a closed contact, otherwise it will run. Hence any wire breakage in the control loop or the MK6E rebooting will start the 88QE.

As stated the overload should be wound to maximum. Prior to each turbine start the 88QE is started and checked for correct operation by the MK6E. Also if the GT is online for more than a week the 88QE is also tested.

Each test checks that the motor has not seized or the pump has become uncoupled. The current draw must be within a certain range. Also the pump output pressure must exceed a certain value, 20psi I think. Failure during the start cycle will abort the sequence and test failure when online is just an alarm.
 
Thanks a lot for your reply 309EGuy

we have a contractor that installed normally open contactor for that and they persist their opinion and says that it doesn't need to be normally close. so Do you have any standard like API,IEC,or Document that i will be able to convince them?

Thanks
 
In our plant, we have DC compound motor for emergency lube oil pump. Since commissioning, overload relay has been intact in control circuit. Kindly advise or guide for bypassing the overload relay in control circuit of Emergency lube oil pump motor. Remember motor is DC compound type.
 
Amjad Ali,

In my experience compound wound DC motors are not uncommon in Emergency L.O. Pump motor applications. So, I'm curious as to why it's so important to solving this problem?

In my experience, the overload relay ONLY monitors the current flowing in the armature circuit, and there is current flowing in the field circuit(s) at all times, to keep the motor warm enough to drive off moisture/prevent condensation--AND to help ensure the motor starts as quickly as possible.

You didn't say what kind of turbine- and control system is being used on this turbine. But, in my experience most overload relays for critical motors are configured to used normally closed contacts that open when an overload exists. In other words, the circuit is "intact" when there is NOT and overload, and is "broken" when there is an overload. So, if I understand your "...overload relay has been intact in control circuit..." (and I'm not sure I do) you are saying that the overload is active at all times whether or not the Emer. L.O. Pump motor is running or not. In that case, and based on my experience, are you certain that the wiring between the turbine control system (which is, I presume, where the alarm is being annunciated) and the overload relay is good--and that the circuit is closed when there is NO overload, and opens when there is an overload?

Because if the alarm is being annunciated when the motor is NOT running, AND the overload is only monitoring the armature current, AND the control system is expecting a closed circuit where there is NO overload, then it could be a simple wiring problem.

Or it could be a configuration input with the control system channel the overload input is wired to.

Or it could be a problem with the sense of a contact in the programmable control system.

But without knowing a LOT more about the turbine and control system and how the Emer. L.O. Pump motor starter and overload relay is configured it's very difficult to say much more.

Please write back to let us know what you find!!!
 
Top