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How to Perform Dynamic Relay Testing on Digital Relays

If you’ve read anything about relay testing written in the last ten years or so, you’ll see a pattern; No-one is talking about the traditional pickup and timing tests most relay testers (and most automated relay testing software) use to test relays. You are much more likely to read terms like “dynamic testing” or “system testing”, which are the true future of relay testing.  Unfortunately, these terms aren’t well defined and are usually embedded in a short article written in engineer-ese that even I, a relay testing “expert”, usually have trouble following.

We briefly covered dynamic testing in The Relay Testing Handbook: Principles and Practice, but I’ve trained hundreds of students since I wrote that book. You might think that my new book (The Relay Testing Handbook: Simplified Motor Relay Testing) only applies to motor relay testing, but it really is a step-by-step guide for dynamic relay testing that you can apply to any relay, from any relay manufacturer, in any application. Motor relays happen to be an excellent entry point to dynamic testing because it’s usually impossible to map a pickup indication to an output in a motor protective relay. This means you have to look for another way to measure pickup, which happens to be a better method for pickup testing on all digital relays.

Here’s an excerpt from the newest entry to The Relay Testing Handbook series that includes everything I’ve learned about dynamic protective relay testing. Look for an email from me in January 2018 that will give you a pre-release discount. If you’re not getting a technical article from me in your inbox every other week, sign up for them in the sidebar, or at the bottom of the page.

Read the Free Excerpt from The Relay Testing Handbook: Simplified Motor Relay Testing

F. Dynamic Pickup/Timing Tests

Most motor protection elements must be performed using a dynamic pickup/timing test because, unlike other digital relays, motor relays typically do not map pickup values as separate logic elements that can be used in testing. Some relay testers get frustrated by the lack of pickup logic, but motor relays opened my eyes to new testing possibilities in normal relays.

We can use the Overload Alarm setting from the Pickup Tests Section of this chapter as an example of a dynamic pickup/timing test. The Overload Alarm Pickup setting is 5.06A. The expected tolerance from the relay manufacturer is ±0.05A. Therefore, the allowable pickup range is 5.01A to 5.11A (not including your test-set error).

You could perform a traditional pickup test to find that the actual pickup is 5.05A, but that number isn’t quite true. You probably increased your current in steps, so your recorded pickup will depend on the size of your steps.

If you have a 6A step and start from zero, your recorded pickup would be 6A. If your step size was 1A, your recorded pickup would be 6A again because the relay didn’t pick up at 5A, but did pickup at 6A. If your step size was 0.1A, your recorded pickup would be 5.1A because the relay didn’t pick up at 5A, but it did pickup at 5.1A. If your step size is 0.01A, your recorded pickup could be 5.07A because 5.06A was just a hair too small, but 5.07A was over the pickup.

The accuracy of your pickup results depends on the resolution of your steps. Smaller step sizes give you better resolution, but increases your testing time. Most relay testers would probably choose a 0.1A resolution as a balance between accuracy and speed. When they obtain that 5.1A pickup test result, the actual pickup was between 5.0A and 5.1A, and the relay tester assumes it passes because of the “small” step size and that it falls into the 5.01A to 5.11A specified range.

A dynamic pickup/timing test starts with the standard step pickup test described previously, and takes it to its logical extreme. If the specified pickup range is 5.01A to 5.11A, any pickup value in that range is a pass, so why should we waste time finding the exact number? Finding exact pickup values in electromechanical relays was important because they can be out of calibration and brought back into calibration with some adjustments. A digital relay can only pass or fail. There are no adjustments.

A dynamic pickup/timing test applies a test state that falls just outside the expected tolerance (5.0A in our Overload Alarm example) and ensures the relay does not operate. We now know that the pickup MUST be greater than 5.0A. That first state is copied and one variable is changed to apply a value on the other side of the element tolerance (5.12A in our Overload Alarm example). The relay should trip when the new state is applied and, if it does, we know the Overload Alarm is somewhere between 5.01A and 5.11A. Any number in that range, whatever the actual value is, will pass.

If you turn on a timer during the second state, you could also measure the element’s time delay to build a timing test into your test plan. One multi-state test could test the pickup and timing for any element in less than a second. The output logic would also be tested if you monitored the in-service contacts.

A dynamic pickup test can be applied to ANY element inside a DIGITAL relay with a FIXED time delay. This test procedure will NOT work with inverse-time elements. You can prevent interference from other elements by adding a Normal State before each test. Some element timing specifications will not apply until you have significantly exceeded the pickup, so you may need to add another state to perform an accurate timing test. A universal dynamic pickup/timing test would look like the following test plan:

  • Apply a Normal State with Nominal Voltage for a time longer than any inverse reset time (5-15s normally).
  • Apply a No-Op State that will not trip just outside the element’s tolerance. The state should stay on longer than the element time delay, plus the time delay tolerance.
  • Apply a Normal State with Nominal Voltage for a time longer than any inverse element’s reset time (5-15s normally).
  • Apply an Op State that is a duplicate of the No-Op State where one variable changes to apply a value just outside the other tolerance.
  • Apply a Normal State with Nominal Voltage for a time longer than any inverse reset timetime (5-15s normally).
  • Apply a Time Test State that is a duplicate of the Op State where one variable changes to apply a value specified by the timing specifications (110% or 120% of pickup, for example).

The current and voltages would not immediately be removed in a real fault or alarm situation in the real world. There will always be a delay as the relay output contact sends a signal to another device, and that device will take some time before it operates. Some test-plans can add a Post-Fault state to:

  • Simulate the previous state to get more accurate targets from the relay.
  • Simulate the previous state to test breaker fail elements.
  • Apply nominal conditions to prevent other protection from operating while you review the relay targeting.
  • Provide a placeholder state at the end of a test to bypass timers as described in the next paragraphs.

A template for these test plans can be created in the State Simulation or State Sequencer of any modern test-set software. However, unlike a traditional test, you may need to perform more than one evaluation: Did the relay operate in the No-Op State? Did it operate correctly in the Op state? Was the time delay correct in The Op State or Timing State? The method for answering these questions depends on your test-set software as described below:

Omicron Test Universe

  • The Omicron Test Universe software requires you to go through all fault states in the order specified. Therefore, you can set the transition for each state to forward to the next state whenever the time delay is exceeded, or the contact closes, whichever comes first.
  • One timer starts when the No-Op State begins and stops when the No-Op State stops. Then an evaluation is set to Pass if the timer matches the state time delay, or fail if the timer is faster than the state time delay.
  • A second timer is set like a traditional time test that starts when the Op State starts and stops when the Op State ends. The evaluation is set to pass if the timer falls within the timing accuracy of the element, or fails when the timer equals the state timer.

Doble Protection Suite

  • Doble’s Protection Suite software allows you to set a transition to move to the next state when the timer expires, or jump to another state when a contact operates. You can set all of the state transitions to move to the next state if the timer expires, or jump to the Post-Fault State if the contact operates.
  • Set a timer that starts when the Op State starts and stops when the relay output operates. The evaluation is set to pass if the timer falls within the timing accuracy of the element.
  • If the element operates in any state other than the Op State, the test will fail because the timer will be bypassed.

Manta Front Panel

  • Manta’s front panel is basically like the state simulation programs from other software packages. You can increase the number of states in the Advanced Setting menu. By default, any relay contact operation stops the test because all inputs are set to go to a Post-Fault State by default, and that state is typically disabled, so the test simply stops when an input operates. However, you could manipulate the settings to follow any pattern you wish.
  • Set a timer that starts when the Op State starts and stops when the relay output operates. The evaluation is set to pass if the timer falls within the timing accuracy of the element.
  • If the element operates in any state other than the Op State, the test will fail because the test stops before the timer has a chance to start.

This is the test-plan style described throughout this book to test motor elements because the element definitions in most relays do not include specific pickup logic. I encourage you to start applying this test procedure to ALL of your digital relay testing to create faster and more effective test plans.

Dynamic testing has additional benefits because it can find problems with relay logic and settings from seemingly unrelated elements that will never be found using traditional testing techniques. Many relay testers often give up on dynamic testing because sometimes an unrelated element operates when they perform a test; so they start changing settings in order to get numbers on their test sheet.

I consider these “problems” to be opportunities. Either the design engineer has made a mistake in the settings that effectively disables an element, or I’m going to learn something. The point of all electrical testing is to find problems before the equipment is energized, and all of your test plans should be designed to find those problems. Dynamic Testing helps you find problems that will never be found with traditional test techniques. If you find a problem; that’s good news because now it can be fixed before someone gets hurt, or equipment gets damaged.

Sometimes the problem is that your test plan sucks. That’s good news as well because now you can learn more about the power system and add new tools to your tool belt. Every new piece of knowledge or every new technique you learn helps you become a more effective tester and increases your future prospects. Every employer wants the best on their team.

The most common example of a test plan that sucks happens when you try to test a phase overcurrent element and the ground overcurrent operates first. Many relay testers get frustrated and start reprogramming the relay at that point. Step back and think about the problem whenever something like that happens instead. If it’s impossible for you to test the phase overcurrent without disabling the ground element, why is the phase element turned on? Think about why two different overcurrent elements are enabled in this relay with different settings. Ground overcurrent elements are for ground faults, and phase overcurrent elements are for phase-to-phase or three-phase faults. If you want to test a phase overcurrent element, simply simulate a phase fault and all your problems magically disappear. It’s easy with modern test-sets.

I’ve added a classic mis-coordination between elements problem in the example relays. I encourage you to read the “Perform a Dynamic Lagging Power Factor Pickup/Timing Test” section in Chapter 24 to see how these problems should be addressed in the real world.

Dynamic relay testing is extensively covered in the How to Test Protective Relays Online Seminar and The Relay Testing Handbook: Principles and Practice. You should never perform a test if you do not know how to evaluate the results correctly.

G. Dynamic Pickup/Timing Test Template for Motor Relay Testing

Relay testing becomes more effective and efficient if you create a master template that can be used for most elements inside a relay. You can break this template into two parts if you wish to make it easier to understand, or if you want to use less sophisticated test-sets. Simply perform a No-Op test plan first to prove that the relay will not trip outside its tolerance, then perform an Op test plan to prove it will trip.

The following template will be used and referred to in the individual element chapters throughout this book.

a) Apply Emergency Restart

You should apply an Emergency Restart before your test to make sure the Thermal Capacity Used bucket is empty, or at 0%. Otherwise, other ALARM elements may interfere with your test result, such as Thermal Capacity Used described in the next chapter.

b) Connect All Relay Outputs Set to Operate to Test-Set Inputs

Enable all inputs in your test-set software that will be connected to relay outputs.

c) Apply a Ready-to-Start State

Always start your tests with the motor stopped and ready to start. The example relays have undervoltage protection, which means that you must apply voltage before you start the motor as per the following plan:

Test-Set Channel

1–Ready State

Mag

Angle

V1 69.28V 0.00°
V2 -120.00°
V3 120.00°
I1 0.000A 0.00°
I2 -120.00°
I3 120.00°
Max Time 5.0000s

The Max Time should be long enough to reset any alarms, LEDs, or messages on the front panel while this state is being applied.

d) Apply a Starting-to-Running State

Most motor protection will not operate correctly unless the relay detects a Running motor state. Therefore, apply some current and wait for the motor to change from Starting-to-Running. That current must be greater than any undercurrent protection, if enabled, and less than the FLA of the motor to minimize impact to the Thermal Capacity Used bucket as described in the Starting Test State section of this chapter.

The following addition to the test plan will give you a running state for your test:

Test-Set Channel

1–Ready State

2–Start/Run State

Mag Angle Mag

Angle

V1 69.28V 0.00° 69.28V 0.00°
V2 -120.00° -120.00°
V3 120.00° 120.00°
I1 0.000A 0.00° 1.000A 0.00°
I2 -120.00° -120.00°
I3 120.00° 120.00°
Max Time

5.0000s

5.0000s

e) Apply a No-Op State Outside the Expected Tolerance

Now that the motor is running, apply a No-Op State that should not operate to make sure the pickup is within the expected tolerance.

Calculate the allowable pickup range using the relay specifications plus your test-set specifications; or use the rule-of-thumb 5% percent or 0.05 absolute tolerances. Apply your test current/voltage/angle/frequency slightly outside the tolerance where the element will NOT operate.

Calculate the allowable time delay range using the relay specifications plus your test-set specifications; or use the rule-of-thumb 5% percent or 0.05 absolute tolerances. Apply a Max Time setting slightly longer than maximum range to give the relay plenty of time to operate. You may want to add another three cycles to this time if the relay manufacturer specifies that the time delay must be at, or above, a certain magnitude that is greater the Op State test magnitude.

Test-Set Channel

1–Ready State 2–Start/Run State 3–No-Op State
Mag Angle Mag Angle Mag

Angle

V1 69.28V 0.00° 69.28V 0.00° ??V ??°
V2 -120.00° -120.00° ??°
V3 120.00° 120.00° ??°
I1 0.000A 0.00° 1.000A 0.00° ??A ??°
I2 -120.00° -120.00° ??°
I3 120.00° 120.00° ??°
Max Time

5.0000s

5.0000s

??s

f) Apply a Buffer State

This state is not really necessary for some tests, but it is often a good idea to put a buffer state between the No-Op State and the Op State to prevent mis-operation caused by another element in the relay operating. This Buffer State looks exactly like the running state in a motor relay and is added after the No-Op State.

Test-Set Channel

4–Buffer State
Mag

Angle

V1 69.28V 0.00°
V2 -120.00°
V3 120.00°
I1 1.000A 0.00°
I2 -120.00°
I3 120.00°
Max Time

5.0000s

g) Apply a No-Op State Outside the Expected Tolerance

Apply a test current/voltage/angle/frequency that should trip using the pickup tolerance calculated in section D. Only one value should change between the Op and No-Op State, therefore the time delay will be the same between the two states.

Test-Set Channel

4–Buffer State 5–Op State
Mag Angle Mag

Angle

V1 69.28V 0.00° ??V ??°
V2 -120.00° ??°
V3 120.00° ??°
I1 1.000A 0.00° ??A ??°
I2 -120.00° ??°
I3 120.00° ??°
Max Time

5.0000s

??s

h) Apply a Post-Fault State

You can use a Post-Fault State in these test plans for the example relays to make sure the 27-Element (Undervoltage) doesn’t operate after the element operates, which will give you time to look at the relay targets and event recorder.

Test-Set Channel

1—Ready State 2—Start/Run State 3—No-Op State
Mag Angle Mag Angle Mag

Angle

V1 69.28V 0.00° 69.28V 0.00° ??V ??°
V2 -120.00° -120.00° ??°
V3 120.00° 120.00° ??°
I1 0.000A 0.00° 1.000A 0.00° ??A ??°
I2 -120.00° -120.00° ??°
I3 120.00° 120.00° ??°
Max Time

5.0000s

5.0000s ??s
Timer

Start = No-Op State Starts

Stop = No-Op State Stops

i) Measure the Time Delay

Set up a timer that starts when you enter the Op State and stops when the relay output operates. Repeat for all outputs programmed to operate during the test.

You should also set a timer or evaluation that ensures that the element does not operate in the No-Op State if your relay test-set software requires it (such as Omicron Test Universe).

Test-Set Channel

4—Buffer State 5—Op State 6—Post-Fault State
Mag Angle Mag Angle Mag

Angle

V1 69.28V 0.00° ??V ??° 69.28V 0.00°
V2 -120.00° ??° -120.00°
V3 120.00° ??° 120.00°
I1 1.000A 0.00° ??A ??° 0.000A 0.00°
I2 -120.00° ??° -120.00°
I3 120.00° ??° 120.00°
Max Time

5.0000s

??s

10.0000s

Timer

Start = Op State Starts

Stop = Relay contact closes

j) Set Up the Transitions Between States

Your test-set software needs to know how to transition between states. Add transition information into your test plan as per the following chart:

 

Test-Set Channel

1—Ready State 2—Start/Run State 3—No-Op State
Mag Angle Mag Angle Mag

Angle

V1 69.28V 0.00° 69.28V 0.00° ??V ??°
V2 -120.00° -120.00° ??°
V3 120.00° 120.00° ??°
I1 0.000A 0.00° 1.000A 0.00° ??A ??°
I2 -120.00° -120.00° ??°
I3 120.00° 120.00° ??°
Max Time 5.0000s 5.0000s ??s

Timer

Start = No-Op State Starts

Stop = No-Op State Stops

Transitions Max Time = next state

Relay Output = Post-Fault

Max Time = next state

Relay Output = Post-Fault

Max Time = next state

Relay Output = Post-Fault

k) Evaluate and Record Your Test Results

Create an evaluation that fails the test if the relay operates in any state other than the Op State. This could include the following scenarios:

  • The test stops when the relay operates in any state. The Op State Timer will not start, which fails the test. (Manta)
  • Any relay output operation causes the test plan to jump directly to the Post-Fault State. The timer never starts if the relay operates before the Op State and the test fails. (Doble)
  • Create two evaluations: One measures the No-Op State timer and fails if it is less than the No-Op State Max Time. One measures the Op State Timer and will only pass if the measured time falls within the expected tolerance. The test will only pass if both evaluations pass. (Omicron)

The pickup is between the No-Op State and the Op State values and should be recorded as a note in the test results. “The element pickup is between the No-Op State and the Op State, which falls within the relay tolerances of X and Y.”

Conclusion

Dynamic Testing can be applied to any relay element with a fixed time delay in any relay.  Once you have one built, it’s very easy to change the voltage/current/phase angle/frequency required for your test.  I highly recommend this technique for relay testing.

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About the Author Chris Werstiuk

Chris is an Electrical Engineering Technologist, a Journeyman Power System Electrician, and a Professional Engineer. He is also the Author of The Relay Testing Handbook series and founder of Valence Electrical Training Services. You can find out more about Chris here.

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