Siemens APT Relays – Analysis of Common Faults and Causes of Relays

1. Overhaul of the sensing mechanism

For electromagnetic (voltage, current, intermediate) relays, the sensing mechanism is the electromagnetic system. The faults of the electromagnetic system are mainly concentrated in the coil and the moving and static iron cores.

(1) Coil fault maintenance

Coil failures usually have coil insulation damage; Inter-turn short circuit or grounding caused by mechanical injury; Because the power supply voltage is too low, the contact between the moving and static iron cores is not tight, so that the current through the coil is too large, and the coil heats up and burns out. When repairing, the coil should be rewound. If the armature does not engage after the coil is energized, it may be that the connection of the coil lead wire falls off, causing the coil to break off. Check out the falling off and weld it on.

(2) Core fault repair

The main core failure is that the armature cannot be sucked after the power is on. This may be caused by broken coils, foreign objects between the moving and static cores, and low power supply voltage. It should be repaired according to the situation.

When energized, the armature is noisy. This may be caused by uneven contact surfaces between moving and static cores, or oil contamination. When repairing, the coil should be removed, filed or smoothed its contact surface; If there is any oil stain, it should be cleaned.

The noise may be caused by short circuit or ring breakage, and it is sufficient to repair or replace a new short circuit ring.

After a power failure, the armature cannot be released immediately, which may be caused by the moving core being stuck, the air gap of the core is too small, the spring is strained, and the contact surface of the core is oily. DURING MAINTENANCE, THE CAUSE OF THE FAILURE SHOULD BE TREATED DIFFERENTLY, OR THE AIR GAP SHOULD BE ADJUSTED TO PROTECT IT AT 0.02-0.05MM, OR THE SPRING SHOULD BE REPLACED, OR THE OIL SHOULD BE CLEANED WITH GASOLINE. In the case of thermal relays, the sensing mechanism is a thermal element. Common faults are burnout of the thermal element, or malfunction and non-operation of the thermal element.

(1) Burning out of the thermal element. This can be caused by a short circuit on the load side, or if the hot element operates too frequently. During maintenance, the thermal element should be replaced and the setting value should be readjusted.

(2) Malfunction of the thermal element. This may be caused by the setting value is too small, the action is not overloaded, or the use of strong shock and vibration, the action mechanism is loose and tripping, resulting in malfunction.

(3) The thermal element does not operate. This may be due to the setting value being too small, which makes the thermal element lose its overload protection function. During maintenance, the setting current should be adjusted according to the load working current.

2. Overhaul of actuator

The actuator of most relays is a contact system. Through its "pass" and "break", a certain control function is completed. The failure of the contact system is generally due to contact overheating, wear, fusion welding, etc. The main causes of contact overheating are insufficient capacity, insufficient contact pressure, oxidation or unclean surface, etc.; The main reasons for the aggravation of wear are that the contact capacity is too small, and the arc temperature is too high to oxidize the contact metal. The main cause of contact fusion welding is high arc temperature or severe contact jumping. The order of service for the contacts is as follows:

(1) Open the outer cover and check the surface condition of the contacts.

(2) If the surface of the contact is oxidized, the silver contact can not be repaired, and the copper contact can be filed with an oily file or gently scraped off the oxide layer on the surface with a knife.

(3) If the contact surface is not clean, it can be cleaned with gasoline or carbon tetrachloride.

(4) If there are burn marks on the surface of the contact, the silver contact does not need to be repaired, and the copper contact can be repaired with an oily file or knife. It is not allowed to use abrasive cloth or sandpaper for trimming, so as not to leave sand particles and cause contact**.

(5) If the contact is welded, the contact should be replaced. If it is caused by the contact capacity being too small, the relay with a large capacity** should be replaced.

(6) If the contact pressure is not enough, the spring should be adjusted or replaced to increase the pressure. If the pressure is still insufficient, the contacts should be replaced.

3. Overhaul of intermediate mechanism

(1) For air-type time relays, the intermediate mechanism is mainly airbags. A common fault is inaccurate delay. This may be due to the airbag being poorly sealed or leaking, which shortens the action delay or even does not delay it; It may also be that the air passage of the airbag is blocked, making the action delay longer. When repairing, the former should be reassembled or replaced with a new airbag, and for the latter, the air chamber should be disassembled, and the blockage should be **.

(2) For speed relays, the bakelite pendulum belongs to the intermediate mechanism. If the motor cannot brake and stop when braking in reverse, it may be that the bakelite pendulum is broken. It should be replaced during overhaul.

Summarizing the common fault repair methods of relays is conducive to the good operation of power equipment and systems, and can also provide reference experience for peers.

Siemens APT Relays – Analysis of Common Faults and Causes of Relays

Siemens APT Relays – Analysis of Common Faults and Causes of Relays

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