Even though time flies and protection systems have been implementing more and more modern and advanced relays, many places still have operation backboned by Electromechanical ones.

Design

First of all, let’s clarify what is, in fact, an EMR, or the Electro-mechanical Relay?

Operation type

These relays typically operate instantaneously, closing as soon as the mechanical motion allows, without any intentional time delay. A time delay can be introduced using mechanisms such as bellows, dashpot, or clockwork escapement, though the timing accuracy of these methods is notably less precise than that of induction-type relays.

EMR relays are generally housed in a semi-flush mounting, draw-out case, which is usually installed on the door of the switchgear cubicle. Installers connect sensor and control wiring to terminals within the case. The relay is then inserted into the case and makes connections via small switches or a bridging plug, depending on the manufacturer’s design.

This setup allows the relay to be disconnected and removed without disturbing the wiring. When the relay is removed, the current transformer (CT) connections inside the case are automatically shorted, which protects the CT secondary winding from overvoltage and potential damage.

Applications

Most commonly they are attached to medium voltage circuit breakers to detect abnormalities in the current flowing within the electrical system. There are no fancy functions or advanced logic to assess the condition of the network. But the simplicity, previous low cost, and rigidity in operation have earned the popularity for EMRs so we can still see a lot of them in operation today.

Many of them are planned for replacement by more compact and advanced electronic and digital ones, but ongoing maintenance is still necessary. So this article will help you answer the question “How to test the electromechanical relay fast and easy?”.

Testing procedure for electromechanical relay

Same as with many types of protection elements that have a mechanical component, it’s important to check the physical condition of modules and parts before moving to the next stage. Maybe a contact is jammed, or some wiring came loose?

Visual Inspection:

1.  Remove the relay cover

   1. Inspect the gasket of the cover

   2. Inspect for cracks or frame tightness

   3. Clean the covers and glass thoroughly

2. Remove the relay assembly from the case

   1. Shortcircuit the CT terminals for safety

   2. Open all of the trip circuits

3. Foreign objects like metal bits and dust should be removed from the case and the relay. These may cause problems with the mechanical parts and erratic operation of the relay.

4. Blow dust by blowing air gently using a hand syringe.

5. Metal bits or corrosion should be removed from the magnet poles or disc using a brush or magnet cleaner.

6. Hold the relay up to the light to ensure that the gap has good clearance and that the disc does not rub.

7. Check for moisture problems. If you see rust spots on the relay, it is important to check if the relay is in proper operational environment. Moisture can cause severe corrosion and problems in the mechanical components.

8. Check for loose connections. Taps, screws, bolts, nuts, and pivotal joints should be tight.

9. The bearings should be smooth. To check, the disc is rotated manually to close the contacts and letting the action of the spiral spring to the relay disc to its de-energized position. You should observe for smoothness and should not be sluggish. Clean and put oil on the mechanism. However, if cleaning and oiling fails, the relay must be reconditioned or replaced.

10. The operation of targets should be manually checked. This is done by fitting the armatures and checking if there is a showing target.

11. The relay coil must be inspected to ensure that it is not subjected to high currents for a long time.

12. The components that touch together during a relay’s normal de-energized position must be cleaned. This is to prevent the relay from getting stuck or operating erroneously, especially on low current faults.

When you’ve finished with the visual and mechanical side it is time to test the electrical.

Electrical Testing:

1. Disconnect the relay from the trip and power circuits for testing.

2. Secondary injection testing.

1. This allows you to check the operation of the circuit breaker, relay connections and the relay assembly.

2. This testing method is conducted by injecting current directly into the relay. 

Tools

What items to use?

For mechanical conditioning a standard handyman set would be enough – have some clippers to cut wires if needed, a brush to clean from dust and particles, and screwdrivers, of course, to mount and secure all connections.

For the electrical test, a standard single-phase or 3-phase injection kit would be sufficient, as the tester relay is quite simple on its own.

Good option would be to use a secodnary testing device that has a standalone voltage source to power up tested relay. THis makes the procedure so much faster and independent from situation on site.

Have any questions or comments – please share to improve the guide.