Power Systems Protection & Control – The Anti-Pumping Relay Application
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Background – The Anti-Pumping Relay Function
In power systems protection, the control circuits of circuit breakers are designed in such a way to prevent the circuit breaker from closing and opening multiple times successively as it will damage the breaker closing mechanism.
Imagine this scenario, the operator turned the control switch in order to to bring the breaker from the open state into a closed state. In this instant, while the control circuit is energized by pressing the close/open (TNC) switch, a fault also occurred that trips open the breaker, without the anti-pumping mechanism the breaker will be caught up in a repeated cycle of close-trip-close operation. Since the closing mechanisms of breakers are not designed to withstand this condition, it will be damaged.
How the Anti-Pumping Relay Works
The figure above is a portion of an actual schematic diagram for a 230kV power circuit breaker. For the purpose of this subject, only focus on the sections that are highlighted in yellow. This portion of the breaker control circuit refers to the close circuit. The close circuit is one that needs to be energized or turned on in order for the breaker to activate it’s closing mechanism to bring the breaker from an open state into a closed state.
First, consider that the breaker is in the open position or non-energize status. All the contacts shown are also in the non-energized state.
In order to close the circuit breaker, we begin by turning the local control switch (item #1) above. This switch is the item that we showed in Figure 1.
Once this happens, the normally open (N.O.) contact of local control switch (item #1) will change from the N.O. state into a Normally Close (N.C.) state. The close relay circuit is then completed and thus energizing the close relay (item #2).
Once the close relay is energized, one of it’s auxiliary switch that is normally open will change state to normally close (item #3). This action will in turn complete the circuit of the closing coil (item #4). Note that the spring position limit switch (item #5) must also be in the close or 2nd position in order for this to happen.
Once the closing coil circuit is completed, the closing coil is energized and will then bring the circuit breaker from the open state into a closed state. At this point, you already have closed the circuit breaker.
Now, imagine that while pressing the close switch, at the same time a fault also occurs and trips open the circuit breaker. Without the anti-pump mechanism, since you are still holding the close switch, it will bring back the circuit breaker to a close status and thus the breaker will be caught up in a rapid close-open-close cycle and damage the mechanism.
Now to continue with the discussion, once the breaker has been brought to a closed state, one of it’s auxiliary contact (item #8) will change from a normally open to a normally close state. Once this happens, the circuit of the anti-pump relay (item #6) will be complete and thus energizing the relay.
Once the anti-pump relay is energized, one of it’s auxiliary contact (item #9) will change state from N.O. to N.C. and thus forming a holding circuit which will keep the anti-pump relay energized even if the circuit breaker auxiliary switch (item #8) turns back to an open state.
At the same time, once the anti-pump relay is energized, another auxiliary contact (item #7) will change state from a normally closed into a normally open. Because this contact or switch is in series with the closing coil circuit, it will open that circuit and thus preventing the closing circuit mechanism from closing back the breaker rapidly.
As an added measure, the manufacturer also added in series two normally closed contact (item #10) into the closing coil circuit. This means that in the instant that the circuit breaker is closed, these contacts will change state from normally close to normally open, and thus de-energizing the closing coil. The intent is the same as the anti-pump relay function. However, in case these contacts fails to do it’s function, it is good to know that the anti-pump relay is there.
As we can see, this simple arrangement of inserting the anti-pumping relay and some of it’s auxiliary switches into the closing circuit of the breaker made the great difference of protecting the closing mechanism from rapidly closing and opening at the instant that there is a fault while the breaker is also being closed.