Load bank

A load bank is a device used to simulate an electrical load so that a generator, UPS, transformer, battery system, or electrical installation can be tested under controlled conditions without connecting the actual plant load.

1. Simple concept

Think of a load bank as an artificial electrical consumer.

For example:

Generator → Load Bank → Electrical energy converted into heat

Instead of supplying a factory, the generator supplies the load bank. The load bank deliberately consumes the generator's electrical output and converts most of it into heat.

2. Why do we need a load bank?

A generator may be rated at 1,000 kW, but if the actual plant load is only 300 kW, simply running the generator at 30% load does not properly demonstrate that it can deliver its rated capacity.

A load-bank test allows you to progressively test:

Test load	1,000 kW generator
25%	250 kW
50%	500 kW
75%	750 kW
100%	1,000 kW

This allows engineers to verify the generator's performance at different loading conditions.

3. What does a load bank actually contain?

A typical industrial resistive load bank contains:

• Resistor elements – create the electrical load.

• Cooling fans – remove the heat produced by the resistors.

• Contactors/switches – select different load steps.

• Control panel – controls and monitors the test.

• Meters – measure voltage, current, kW, frequency and sometimes power factor.

• Protection systems – overtemperature, overcurrent, emergency shutdown, etc.

For example, a 1 MW load bank may have selectable steps:

100 + 100 + 200 + 200 + 400 kW

allowing the operator to apply different combinations of load.

4. Types of load banks

There are three common types.

A. Resistive load bank

Most common for generator testing.

It produces approximately:

kW = kVA × power factor

For a purely resistive load:

Power factor ≈ 1.0

So a 500 kVA resistive load bank approximately produces a 500 kW load.

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B. Reactive load bank

Uses inductors or capacitors to create reactive power.

It is useful when you need to test:

• kVAR

• power factor

• alternator excitation

• voltage regulation

• reactive-load performance

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C. Combined resistive/reactive load bank

Can apply both real and reactive power.

For example:

500 kW + 375 kVAR

This is useful for more comprehensive generator and electrical-system testing.

5. Example: testing a diesel generator

Suppose your plant has:

Generator rating = 1,000 kVA
Power factor = 0.8

The corresponding real power rating is:

1,000 kVA × 0.8 = 800 kW

During testing, you might progressively apply:

25% → 50% → 75% → 100%

At 100%:

800 kW load

The engineer monitors:

• Voltage

• Current

• Frequency

• kW

• kVA

• kVAR

• Power factor

• Engine coolant temperature

• Lubricating-oil pressure

• Exhaust temperature

• Fuel consumption

• Generator winding temperature

This gives a much better picture of the generator's condition than simply starting it for a few minutes.

6. Load bank and energy efficiency

This is particularly relevant to your energy-management work.

A load bank itself does not save energy. In fact, it intentionally consumes energy.

Its value is in testing and verification.

For example, suppose a standby generator normally operates for only 10–20 minutes during routine checks. The generator may never reach a meaningful operating load.

A controlled load-bank test can verify whether:

Generator → engine → alternator → electrical output

is operating correctly at different load levels.

It can also identify:

• poor fuel efficiency,

• voltage instability,

• frequency instability,

• cooling problems,

• alternator problems,

• protection-system problems,

• inadequate generator capacity.

7. Important distinction: load bank vs actual plant load

This is an important concept.

Actual plant load:

Generator → Motors + Pumps + Fans + Lighting + Process Equipment

Load-bank test:

Generator → Load Bank

The load bank is therefore a test instrument, not normally part of the production process.

8. One important issue for diesel generators

For diesel generators, prolonged operation at very low load can be undesirable. Depending on the engine and manufacturer requirements, sufficiently loaded operation can be important for maintaining proper combustion and avoiding problems associated with light loading.

A load bank can therefore be used as part of a generator maintenance and performance-testing programme.

In one sentence

A load bank is an artificial electrical load used to safely and controllably test the capacity, performance, stability and reliability of an electrical power source without depending on the actual plant load.