Overcurrent relay (application examples)


		WARNING
		Death or severe injury can occur if the appropriate safety instructions are not observed. The COMPANO 100 test set can output life-hazardous voltages and currents. Before operating any such electrical equipment, carefully read the Safety Instructions chapter in this manual (see Safety instructions).

This example outlines the working steps for acquiring the pick-up and drop-off current values of a non-directional overcurrent relay as well as the trip times of the relay at different currents. Using the QUICK application module, this test is performed manually. Using the FLEX application module, the test searches for the point where the relay trips instantaneously.

Connect COMPANO 100 to the overcurrent relay

In a substation, the relay’s input would be connected to a current transformer (CT) in order to monitor the current on the power line. To test the relay, connect these inputs to the COMPANO 100 current output I OUT instead. Polarity does not matter for this tests. Plug in the angled cable connectors to the COMPANO 100, and the retractable sleeve connectors to the relay. For many relay types, this allows you to connect without having to use additional adapters.
In a substation, the relay’s output (trip contact 51) would be connected to a circuit breaker (CB) to trip the breaker in case of a detected overcurrent. To test the relay, connect its output to a BINARY INPUT of the COMPANO 100 (IN 1 or IN 2).

Testing an overcurrent relay with QUICK

In the following example, the relay does not have a dedicated pick-up contact, therefore determine the pick-up by checking the display of the relay.

hiddenDetermine and record the pick-up current

Turn the jog dial wheel until I OUT has the focus.
Press the jog dial wheel to enter the I OUT field in edit mode. Then turn the wheel to set the value to the nominal current of the relay under test.

Press the Start/Stop key (now illuminated green).
The I OUT field shows the measured value of the presently flowing current. Pressing the jog dial wheel at this point returns you to the edit mode showing the currently set value. Turning the wheel changes that value. Pressing the jog dial wheel again returns you to the display mode.

Make sure you are in the edit mode at I OUT. Press the jog dial wheel if you are not. Now turn the jog dial wheel very carefully clockwise to increase the current value at I OUT until the relay shows a pickup on its front-panel. Most relays have an indicator for that.
Press the Keep result soft key to record the pick-up current value.

Determine and record the drop-off current value

You should still be in the edit mode at I OUT.

Else, turn the jog dial wheel until I OUT has the focus, and press the jog dial wheel to enter the I OUT field in edit mode.
Turn the wheel very carefully counter-clockwise to decrease the current value until the pick-up indicator at the relay changes its status again. Now you have reached the drop-off current value of the relay.
Press the Start/Stop key to end the test, and to stop the current output. By stopping the output you automatically record the result; there is no need to press the Keep result soft key. At the upper left-hand side of the QUICK application module screen you see the figures 1 2, indicating that you have made two manual recordings.

Determine the trip times of the relay at different currents

Whenever you need to configure a timer, press the Configuration key. However, by default the timer starts on a value change, and stops when COMPANO 100 detects a change at its binary input IN 1. Therefore, there is no configuration required for this test example.

Set an output current higher than the pick-up value in the manner described above.
Press the Start/Stop key (now illuminated green). The timer starts running.
COMPANO 100 outputs the set current. The relay trips after a certain time span that depends on its setting, and closes the trip contact 51.
The closing trip contact has three effects on the COMPANO 100 test set:
- It stops the current output. Reason: by default, the QUICK application module is configured to trigger with a change at the IN 1 binary input (reflected by the symbol at the lower right-hand side of the QUICK screen).
- It stops the timer. Reason: when COMPANO 100 stops the current output, it also stops the timer.
- As the output was stopped, it automatically records the result.

The timer now shows the result of the test: a trip at a specific current after a specific time. Compare the acquired results with the wanted behavior of the relay.

Press Continue to repeat the test with different currents. For many relays, this results in times that are shorter the bigger the current is.


NOTICE
Relay damage caused by too high current. Before you start working with higher currents, set a timeout. A timeout guarantees that the test set switches off after a certain time if there is no trip signal from the relay.

Set a timeout:

In Navigation Mode, turn the jog dial wheel until Timeout has the focus.
Press the jog dial wheel to enter the Timeout field.
Then turn the wheel to set the value to, for example, 5 s.

Press the QUICK key to return to the QUICK application module. Now you can repeat the test with different currents, say 20 A, 50 A and 100 A.

Test results

After the tests, move the focus to the top line of the screen. Press the Previous soft key to browse through the results recorded earlier.

If you would like to save the test results, open the black USB and Ethernet compartment cover at the COMPANO 100 front panel. There you will find a USB port. Insert an USB stick and save the result in XML format to that stick (see Save).

Testing an overcurrent relay with FLEX

This chapter provides you with an example of how to search for the point where the relay trips instantaneously. To do so, use a pulse ramp.

A typical overcurrent-time characteristics:

↑ ms
...	→ A

The point where the relay trips instantaneously is at around 50 A.

Start the search with a current of, say, 2 A below the expected value; in this case 48 A. Then ramp up to 2 A above the expected pick-up value (52 A) in steps of 0.5 A. The relay is expected to trip within approx. 100 ... 200 ms. Depending on the reset characteristics, typically needed reset times can vary between 500 ms and several minutes. In this example we assume a rotating disk, therefore we grant the relay 20 s between two shots.

Before searching for the pick-up value, bring the relay into a stable condition by applying a pre-fault condition. In this example, we apply 4.5 A to achieve this. To do so, define a first ramp state with an output current below the nominal current of the relay under test.

Enter the FLEX mode by pressing the FLEX key.
Use the jog dial wheel to set an output current below the pick-up current of the relay under test. In this example that is 4.5 A.
Turn the jog dial wheel to put the focus onto the top of the screen on sequence step 1. Press the Add state soft key.

Then press the Next soft key to proceed to the next tab to the right. This tab defines the transition from the first to the second sequence step. Define the transition to be a Step.

Proceed to sequence step 2.
In sequence step 2, define the value for the pulse ramp to start. As mentioned above, set a current of 48 A for I OUT, and a timeout of 1.0 ms.

This intermediate sequence step is not to really to output the ramp; it is rather initiating the starting point of the following transition.
Turn the jog dial wheel to put the focus onto the top of the screen on sequence step 2 and press the Add state soft key to add sequence step 3. Press the Next soft key to navigate to the transition after sequence step 2.
Now start generating a pulse ramp that slowly increases the output current until you reach that value that makes the relay switch off with maximum speed (I>>, "high setting"). Because some overcurrent relays do not have a separate output for the instantaneous trip signal, you need to use the trip signal to find out that value. This will slow down the process a bit. In this example we use a pulse ramp. As a result, you will acquire the current value that makes the relay switch off at its high setting.

The pulse ramp of the transition sequence step from sequence step 2 to sequence step 3 could look like that:
- The pulse ramp starts by putting out the value of sequence step 2, in this case 48 A for a time of 200 ms.
- If the relay does not trip within these 200 ms, the pulse ramp then resets the relay by applying a current of 4.5 A for 20 seconds.
- After that the pulse ramp outputs 48.5 A for 200 ms, and so on.
Turn the jog dial wheel to put the focus onto the top of the screen onto the pulse ramp symbol. Press the Next soft key or turn the wheel to proceed to sequence step 3. In sequence step 3 now define:
- The end value of the ramp; in this example that will be 52 A.
- The trigger condition to end the ramp; in this example a toggle on input IN 1.
Press the Start/Stop key to run the sequence of steps.

You will get to see the result in step 3. At I OUT, you see the value where the relay tripped.