What Is No Load Power?

No Load Power (English No Load Power) refers to the power consumed by a resistance furnace when it is operated without a workpiece at the rated temperature.

No-load (transformer) refers to the working state when the primary winding of the transformer is connected to the power supply and the secondary winding is open. At this time, the current in the primary winding is called the no-load current of the transformer. No-load current generates a no-load magnetic field. Under the action of the main magnetic field (that is, the magnetic field that cross-links the first and second windings at the same time), the electromotive force is induced in the first and second windings. [1]

When the transformer is running at no load, although there is no power output on the secondary side, the primary side still draws part of the active power from the power grid to compensate for the magnetic flux saturation caused in the iron core.

The working states of the circuit include: a loaded state, a no-load state, and a short circuit state. Their respective characteristics are described below.

Transformer loss is an important performance parameter of the transformer. On the one hand, it indicates the efficiency of the transformer during operation, and on the other hand, it indicates whether the performance of the transformer in the design and manufacture meets the requirements. Transformer no-load loss and no-load current measurement, load loss and short-circuit impedance measurement are routine tests of transformers.

The no-load test of a transformer is to apply the rated voltage from any set of coils of the transformer. With the other coils open, measure the no-load loss and no-load current of the transformer. No-load current is expressed as a percentage of its rated current.

1. No-load test is to measure the no-load loss and no-load current at the rated voltage. During the test, the high-voltage side is open, and the low-voltage side is pressurized. The test voltage is the low-voltage side rated voltage, the test voltage is low, and the test current is a percentage of the rated current. A few or a few thousandths.

2. Selection of the power capacity of the transformer no-load test: ensure that the power waveform distortion does not exceed 5%, and the no-load capacity of the test product should be less than 50 of the power capacity; use the pressure to adjust the pressure, and the no-load capacity should be less than the regulator 50% of the capacity; when using the generator set test, the no-load capacity should be less than 25% of the generator capacity.

The test voltage of the no-load test is the rated voltage on the low voltage side. The no-load test of the transformer mainly measures the no-load loss. No-load loss is mainly iron loss. The magnitude of iron loss can be considered to be independent of the size of the load, that is, the loss at no load is equal to the iron loss at the load, but this refers to the situation at the rated voltage. If the voltage deviates from the rated index, since the magnetic induction strength in the transformer core is in the saturation section of the magnetization curve, the no-load loss and no-load current will change sharply. Therefore, the no-load test should be performed at the rated voltage.

Note: When measuring the no-load or load loss of large transformers, because the power factor is very low, cos can be less than and equal to 0.1. Therefore, a wattmeter with a low power factor must be used.

3. Through the no-load test, the following defects of the transformer can be found: poor insulation between silicon steel sheets. Local short-circuit burns between core poles and between pieces, core bolts or binding of steel belts, pressure plates, upper yoke, etc. are damaged and short-circuited, silicon steel sheets in the magnetic circuit are loose, misaligned, and the air gap is too large. Multi-point grounding, coils have inter-turn, inter-layer short-circuits or unequal turns of parallel branches, misuse of high-quality and inferior silicon steel sheets or incorrect design calculations ^[1]

No Load Power (English No Load Power) refers to the power consumed by a resistance furnace when it is operated without a workpiece at the rated temperature.

The low no-load power indicates that the furnace has good insulation performance and less heat loss from the furnace.

After no-load power is applied to the oven, it is measured when the resistance furnace is at the rated temperature and has reached the thermal stable state, which is generally 15% of the rated power.