Risks of electrical surges

Lightning discharges could contain currents of 200,000A which if struck at or near power transmission lines would generate a significant voltage transient. This voltage transient could cause significant damage to both domestic and commercial electronic equipment.

These transients can cause damage ranging from the premature ageing of equipment, logic failures and down time, to the complete destruction of equipment within the entire electrical installation. Products such as LCD screens, data servers and industrial equipment such PLC’s are critical to business activity. Protecting this equipment may now be a necessity.

Surge protective devices (SPD) assist in the protection of valuable electrical and electronic equipment against transients, originating from lightning and also from switching sources.

BRITEC SPD range of solutions may offer protection to prevent damage to this sensitive equipment by diverting the damaging transient over-voltages. In the majority of cases this will eliminate equipment failures and reduce downtime.

Terminology & selection criteria

Surge protection devices are classified according to their standard into different types:

• Type 1 – SPD which can discharge partial lightning current with a typical waveform 10/350 μs. Usually employs spark gap technology.

• Type 2 – SPD which can prevent the spread of overvoltage in the electrical installations and protects equipment connected to it. It usually employs metal oxide varistor (MOV) technology and is characterized by an 8/20 μs current wave.

• Type 3 – These SPDs have a low discharge capacity. They must therefore only be installed as a supplement to Type 2 SPD and in the vicinity of sensitive loads. Type 3 SPD’s are characterized by a combination of voltage waves (1.2/50 μs) and current waves (8/20 μs).

Iimp – Impulse current of 10/350 μs waveform associated with Type 1 SPD.

In – Surge current of 8/20 μs waveform associated with Type 2 SPD.

Up – The residual voltage that is measured across the terminal of the SPD when In is applied.

Uc – The maximum voltage which may be continuously applied to the SPD without it conducting.

Selection of suitable devices

Type 1 SPD is often referred to as equipotential bonding SPD’s and are fitted at the origin. A lightning protection system employing these devices only, offer no effective protection against failure of sensitive electrical and electronic systems. In order to achieve this, additional coordinated devices will have to be employed.

A Type 1 SPD is used at the origin of the installation, a Type 2 SPD is used at distribution boards and a Type 3 SPD is used near terminal equipment.

Surge protection needs to be selected such that their voltage protection level (Up) is lower than the impulse withstand capability of the equipment to be protected. This for a 230/400V installation suggests that the value should not exceed 2.5kV.

Connection

To gain maximum protection from the SPD, the connecting conductors should be kept as short as possible. This is to minimize any additive voltage drops on the connecting cables.

The connecting conductors of the SPD shall have a cross sectional area of not less than 4mm2 copper and the total connecting lead length (a+b) should preferably not exceed 0.5m but shall in no case exceed 1m.

Should the distance between the SPD and the sensitive equipment to be protected be greater than 10m, oscillations could lead to higher voltage values appearing at the equipment. Consideration should be given to additional coordinated surge protection devices closer to the equipment.

Protection against SPD short circuits is often provided by an over-current protective device such as a fuse or circuit breaker. This device must of course permit the flow of surge current through the device without operating.

Inspection & Testing

During the Initial Verification or as part of a periodic inspection & test, the SPD should be inspected to ensure it is operational.

There is usually some kind of visual indication on the SPD that the device is still operational. This may be indicated by a GREEN visual indicator window. Should this window indicate RED then it is an indication that the device has reached its ‘End of Life’ and needs replacing. With some products, this will involve the replacement of the device, but on many of the products in the range, this can simply be carried out by replacing the removable cartridge.

SPD quick selection guide

The following is a quick selection guide which may assist in choosing whether SPD’s are required and the correct type of device

• Does the installation contain a lightning protection system?

• Is the installation adjacent to any tall structure, tall trees or near a hill top in a lightning prone area?

• Does the installation contain equipment where higher reliability from overvoltage is required.

If the answer is YES in the above to the first two questions, it is recommended to install a Type 1+2 device. This will provide protection against surges caused by direct lightning strikes and provide protection against transient over-voltages caused by indirect lightning strikes or by switching events.

If the answer is YES to the third question then it is recommended to install Type 2 devices to provide protection against transient over-voltages caused by indirect lightning strikes or by switching events.

Benefits of using BRITEC SPD’s

Product configuration:

• Thermal and dynamic disconnection

• Increases equipment life (by providing clean power)

• DIN mounted devices

• Removable tabs on replaceable cartridges to give the contractor the option of allowing the consumer to replace the cartridge

• IP20

• Does not disconnect your installation from supply when experiencing a transient over-voltage

• Conforms to EN61643-11，EN61643-31，EN61643-21