How to check a transformer with a multimeter? Instructions

It is often necessary to familiarize yourself in advance with the question of how to test the transformer. After all, if it breaks down or is unstable, it will be difficult to find the cause of the equipment failure. This simple electrical device can be diagnosed with a conventional multimeter. Consider how to do this.

What is the equipment?

How to test a transformer if we do not know its design? Consider the principle of operation and a variety of simple equipment. The magnetic core is wound with copper wires of a certain cross-section so that the terminals for the supply winding and the secondary wire remain.

The energy is transferred to the secondary winding in a non-contact way. Here it is almost clear how to test the transformer. Similarly, the usual inductance is called with an ohmmeter. The turns form a resistance that can be measured. However, such a method is applicable when the predetermined value is known. After all, the resistance can change more or less as a result of heating. This is called interturn closure.

Such a device will no longer produce a reference voltage and current. The ohmmeter will show only a break in the circuit or a complete short circuit. For additional diagnostics, a short circuit test is used with the same ohmmeter. How to check the transformer without knowing the winding leads?

This is determined by the thickness of the outgoing wires. If the transformer is lowering, the lead wires will be thicker than the feeders. And accordingly, on the contrary: the input lead is thicker. If the two windings are output, then the thickness may be the same, this should be remembered. The surest way to look at the marking and find the technical characteristics of the equipment.

Kinds

Transformers are divided into the following groups:

• Decreasing and increasing.
• Power is more often used to reduce the supply voltage.
• Current transformers for supplying the consumer with a constant current value and keeping it in a predetermined range.
• Single- and multiphase.
• Welding purposes.
• Pulsed.

Depending on the purpose of the equipment, the principle of approach to the question of how to check the transformer windings also changes. A multimeter can only ring small devices. Power machines already require a different approach to fault diagnosis.

Vertebra method

The ohmmeter diagnostic method will help with the question of how to test the power transformer. The resistance between the terminals of one winding begins to ring out. This establishes the integrity of the conductor. Before this, the body is inspected for the absence of deposits, as a result of heating of the equipment.

Next, measure the current values in Ohms and compare them with the passport values. If they are not available, additional voltage diagnostics will be required. It is recommended to call each terminal with respect to the metal case of the device, where the ground connection is connected.

Before carrying out the measurements, all the ends of the transformer must be disconnected. It is recommended to disconnect them from the circuit for their own safety. Also check the presence of an electronic circuit, which is often present in modern power models. It should also be bottled before checking.

Infinite resistance speaks of an entire isolation. Values of several kilograms already raise suspicions of breakdown on the case. It can also be due to accumulated dirt, dust or moisture in the air gaps of the device.

Under tension

Tests with fed power are conducted when there is a question about how to check the transformer for an interturn closure. If we know the value of the supply voltage of the device for which the transformer is intended, then measure the idling speed with a voltmeter. That is, the lead wires are in the air.

If the value of the voltage differs from the nominal value, then conclusions are drawn about the inter-turn fault in the windings. If the device is cracked or sparked during operation, it is better to switch off such a transformer immediately. It is defective. There are permissible deviations in the measurements:

• For voltage values may differ by 20%.
• For resistance, the norm is the spread in values of 50% of the passport values.

Measurement of ammeter

Let's see how to check the current transformer. It is included in the chain: regular or actually manufactured. It is important that the current value is not less than the nominal value. Ammeter measurements are made in the primary circuit and in the secondary circuit.

The current in the primary circuit is compared with the secondary readings. More precisely, the first values are divided into those measured in the secondary winding. The transformation coefficient should be taken from the reference book and compared with the calculations obtained. The results should be the same.

The current transformer can not be measured at idle. On the secondary winding in this case, too high a voltage can be formed, which can damage the insulation. Also, observe the polarity of the connection, which will affect the operation of the entire connected circuit.

Typical malfunctions

Before checking the microwave transformer, we will give the frequent types of breakages eliminated without a multimeter. Often, power supplies fail due to a short circuit. It is installed by examining the circuit boards, connectors, connections. Less often, there is a mechanical damage to the transformer case and its core.

The mechanical wear of the transformer terminal connections occurs on moving machines. Large supply windings require constant cooling. In its absence, overheating and reflow of insulation are possible.

TDKS

Let's figure out how to test a pulse transformer. Only the integrity of the windings can be established by an ohmmeter. The operability of the device is established when connected to the circuit, where the capacitor, the load and the sound generator are involved.

A pulse signal in the range from 20 to 100 kHz is started on the primary winding. On the secondary winding, measurements are made by the oscilloscope. Establish the presence of pulse distortions. If they are not available, they draw conclusions about a working device.

Distortions of the oscillogram speak of spoiled windings. It is not recommended to repair such devices on your own. They are set up in the laboratory. There are other schemes for testing pulse transformers, where the presence of resonance on windings is investigated. Its absence indicates a faulty device.

It is also possible to compare the shape of the pulses applied to the primary winding and output from the secondary winding. A deviation in shape also indicates a malfunction of the transformer.

Several windings

To measure the resistance, the ends of the electrical connections are released. Choose any output and measure all the resistance relative to the others. It is recommended that you write down the values and mark the checked ends.

So we can determine the type of winding connection: with the average leads, without them, with a common connection point. More common with a separate connection of windings. Metering can only be done with one of all wires.

If there is a common point, then the resistance will be measured between all available conductors. Two windings with an average pin will only have values between three wires. Several conclusions are found in transformers designed to work in several networks rated at 110 or 220 volts.

Nuances of diagnosis

The hum at the operation of the transformer is normal, if it is a specific device. Only sparking and crackling indicate a malfunction. Often, heating the windings is normal operation of the transformer. More often this is observed in lowering devices.

A resonance can occur when the transformer housing vibrates. Then it should be simply fixed with insulating material. The operation of the windings varies considerably with loose or contaminated contacts. Most of the problems are solved by sweeping the metal to a shine and a new tightening of the leads.

When measuring the voltage and current values, account should be taken of the ambient temperature, the magnitude and nature of the load. The control of the supply voltage is also necessary. Checking the frequency connection is mandatory. The Asian and American technology is rated at 60 Hz, which leads to low output values.

Inadvertent connection of the transformer can lead to malfunction of the device. In no event is DC voltage connected to the windings. The threads will quickly melt otherwise. Accuracy in measurements and competent connection will help not only to find the cause of the breakdown, but, perhaps, to eliminate it in a painless way.