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10 most common causes of electrical failures

 

The electrician in his practice is faced with completely different cases, which sometimes reach the point of absurdity. After all, you can never foresee what might happen to electrical equipment during its operation. Equipment is three-phase and single-phase - these types are most common.

However, it is worth noting that their breakdowns are either the same or have similar causes. The most common element in the electrical equipment of an industrial enterprise was and remains (perhaps forever) an electric motor, let's look at the causes of their breakdowns.

10 most common causes of electrical failures

Problems with electric motors

Situation: voltage comes to the electric motor, but it does not work or does not work properly. Start inspecting the boxes on the motor housing where the cable is supplied and disconnecting the star or triangle circuit.

Problems with electric motors

Causes:


1. Oxidation or burning of contacts. We need to clean them and make a test run of the electric motor, if this did not happen, we proceed to further diagnostics.


2. Open phase windings. if you have clamp meter, measure the current at each phase, it will become clear to you whether at least one of the windings consumes current. If there is no neutral wire, then when two of the three windings break, the current will not be consumed by any of them.

The cause of the breakage may be: mechanical impact or electric shock, overheating, the effects of inter-turn circuit. Such an engine is not subject to operational repair - the only option is its replacement and further rewind.


3. Inter-turn closure. The engine starts to rotate, gradually slows down, does not hold the load, works with increased noise. The diagnosis is confirmed by elementary - clamp meters, the current in each phase is measured, if on one of them the current is significantly different from the others - this is most likely the reason.

Pay attention to the current. You can verify with the nominal by reading its value on the plate with technical data. The causes of this malfunction: a blow to the electric motor, humidity and water, start-up after a long downtime.

Engine data plate

After prolonged inactivity, the electric motor should be dried before being put into operation. The fact is that inside the engine humidity can increase, which entails a decrease in insulation resistance, and this leads to stray currents, increased heating and, as a result, a breakdown of insulation at the place of its overheating.

This can be done by removing one of the engine covers and directing the heat gun toward it for a long period of time - from units of hours to several days depending on size.

By insulation resistance, you can check the readiness of the engine for work. Normal consider insulation 1 MΩ per 1000 V, i.e. for a three-phase motor rated at 380 volts, there must be a resistance of at least 0.5 megohms. Actual values ​​are usually larger, from 2 megohms to “infinity”.

If the motor is small, up to 1 kW, you can completely disassemble it, remove the rotor and put an incandescent lamp at 100-150 W in the stator. There are methods for drying the windings with alternating current, through a step-down OR autotransformer. The method consists in applying a small voltage, the windings will start to heat up.


4. Breakdown or short circuit to the housing. The engine can work without any deviations, this option is even more terrible - there is a great danger of electric shock when you touch the metal parts of the housing, engine mounts and actuators. The solution, as well as the causes of this problem is similar - replacement and rewind.

Repair and rewind of an electric motor

5. The rotation of the shaft is difficult, the engine is gaining speed very slowly, and if it starts up under load it may not move at all. Most likely, the grease on the bearings, or rotor bushings, has dried, it is necessary to restore the sliding properties. The reason was natural production, work in conditions of elevated temperature or humidity.

Engine Bearing Lubrication

Causes of malfunctioning electric heaters

There are different types of electric heaters, it's like heat guns with heating elements or spirals, electric fireplaces with nichrome heaters, electric boilers with heating elements, regardless of the type of appliance malfunctions they have are typical:


1. Blown spiral. It occurs either due to natural aging, or due to work in the wrong conditions. If a spiral of greater power was installed during the previous repair, the dimensions of the heater housing may not be enough for its natural cooling, due to overheating it will quickly become worthless.

To be replaced or temporary bolted at the point of break. However, often such a solution will either fail quickly or fail at all - the old nichrome from overheating becomes brittle, and you simply will not pinch it under a bolt.

Electric furnace heating coil

2. Breakdown of the heater in the housing. It is possible when working with the fan turned off, in the case of a heat gun, when working without water, in the case of an electric boiler, due to factory defects, or after a resource has expired. The solution is to replace the heating element, although it may continue to heat up, the phase potential will most likely be present on the body of the electrical appliance.


3. The breakdown of the heating element. Causes and repairs are similar to the previous one.



Problems with cable lines

A common cause of malfunctioning electrical appliances is a lack of voltage. It occurs due to breakage or poor contact of the cable at the connection points.


1. Broken or broken cable. Cables are often broken or interrupted under operating conditions, for example, during construction or dismantling of various structures, as well as due to gusts of wind and improper laying. To avoid this, it is necessary to lay the cable in obviously safe and remote from work places.

When laying cable through floors and walls, use special transitions in the form of iron pipes. And when forwarding the cable through iron masts and structures - to lay rubber or other dielectric in the place of their contact. This will prevent breakdown to the ground.


2. Poor twisting. In the jargon of electricians there is the phrase “make a stock, moor”. It is not always possible to measure the right amount of cable from the sleeve and lay it in one piece, very often you have to type the right length from existing cables.

Therefore, there is a need to connect the cable, although twisting has long been prohibited by the PUE, but even experienced electricians do not disdain this way, either because of the lack of funds for bolt, sleeve, terminal and other types of connections, or because of the human factor (Laziness) .

If there is no voltage on the cable, immediately check the integrity of the connections, sometimes there is a bad contact, or a broken contact of aluminum and copper. Then proceed with the search for kinks and damage to the outer insulation. If you need to connect aluminum with copper, it is better to use a bolt with washers, as shown in the photo.

Connection of aluminum with copper through a bolt with a washer

The washer between the aluminum and copper wires will provide electrical contact, but will exclude direct contact of copper and aluminum. It is undesirable, because when moisture enters such a compound, chemical reactions occur as a result of which corrosion occurs and the contact is destroyed.

Contact damage due to corrosion

Take a look at the top photo, copper veins have found a dark coating with greenish oxides, and aluminum has darkened, such a twist will not work for a long time, and it will not provide reliable contact.

Burnt twists

With a break, short-circuiting of one or more phases to the ground or between each other can occur. What control equipment should respond to - primary or secondary current relays.

Repair of electrical equipment at an industrial enterprise

conclusions

There is an old joke among electricians, which even experienced university teachers do not disdain:

“Electricity is the science of contacts, and there are only two faults:

1. There is contact where it should not be.

2. There is no contact where it is needed. ”

Therefore, most problems in electrical circuits can be diagnosed with the help of dialing and a megaohmmeter, and in rare cases - current clamp. In total, we described 10 causes of various malfunctions of electrical circuits and devices, as well as the main points of diagnosis and repair.

See also on our website: What is a megaohmmeter and how to use it correctly

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