Page 128 - E24 Electrical Notebook

124 - Power Surge Protection & Regulations
High Current - High Voltage - Short Duration
Impulses - Power Surges!
These are all terms to strike fear into the minds of all electrical and
electronic system designers and installers. It is time and more importantly
it is a requirement to act to reduce or eliminate these risks. However, it
seems that cost and competition are significant factors in ignoring the
need for effective and co-ordinated protection. These rarely seen or often
undetected threats originate from many sources:
• An indirect Lightning Stroke, some kilometres away is looking for an
easy path to earth and will find a route through a building
• A direct Lightning Stroke, where a portion of the discharge current
into the lightning protection system or other conductive materials will
attempt to flash over into the internal installations
• The effect of Electrical Switching, caused by utilities, isolation arcing,
electrical motor cycling or sudden changes in electrical flow
There is little we can do to ensure that faults are not created and certainly
nothing to prevent the randomness and unpredictability of lightning
strikes. However, although we cannot eliminate the many and varied
causes, we can certainly reduce their effects.
Surge Protection Devices are designed to specifically protect electrical
and electronic equipment from these spikes and transients. They can
improve reliability, availability, maintainability and safety, all resulting in
the reduction of lost production time and fewer repairs, together with less
data and information loss, thereby improving productivity and profitability.
The extra cost may be a fraction more, but with a significant reduction in
ongoing expenditure, the savings more than make up for the initial outlay.
The Power Utilities external surge arresters provide good primary
protection, but long lead length, installation mistakes and supply
variances can cause a problem to the user that is not necessarily
recognised by the utility. Surge Protection Devices within the facility are
therefore necessary.
The Lightning Protection Systems where fitted offer a good protection
provided the earth bonding is good throughout the facility.
Standards and Regulations make it a clear requirement for Surge
Protection Devices.
BS 7671:2008 IET Wiring Regulations 17th Edition
Section 443: Existing protection against overvoltage of atmospheric
origin or due to switching
Section 534: Deals with the installation of surge protection devices
(SPDs) where required
BS EN 62305 Series of Standards defines the Protection against Lightning
Part 1 - General Principles for Protection of Structures against Lightning
Part 2 - Risk Management
Part 3 - Physical Damage to Structures & Life Hazard
Part 4 - Electrical and Electronic Systems within Structures
BS EN 61643-11
Requirements and tests for Low Voltage Surge Protection Devices
connected to low voltage power distribution systems
BS EN 61643-12
Selection and application for Low Voltage Surge Protection Devices
connected to low voltage power distribution systems
BS EN 61643-21
Requirements and tests for Low Voltage Surge Protection Devices
connected to telecommunications and signalling networks
BS EN 61643-22
Selection and application for Low Voltage Surge Protection Devices
connected to telecommunications and signalling networks
PD Devices is a UK based in-house manufacturer of Surge Protection Devices offering a full range of products including the key Metal Oxide Varistor element.
This allows full customisation at standard product pricing.
PD Devices Ltd Tel : +44 (0) 1364 649248
Unit 1 Old Station Yard Fax : +44 (0) 1364 649250
South Brent
Devon Email : info@pddevices.co.uk
TQ10 9AL Website : www.pddevices.co.uk
Surge Protection Device Co-ordination
BS 7671 and BS EN 62305 require the co-ordination of SPD, where the
latter standard considers the installation of the correct device to limit the
transient overvoltages at the appropriate location within the building.
To facilitate this, the building is partitioned by areas or zones (Lightning
Protection Zones) for which the SPD with the recommended overvoltage
suppression is intended for installation. Zones are based on the degree
of risk and to provide a method that ensure the protection of the equipment.
Zone LPZ 0 is outside the structure of the building and subject to the
severest threat of lightning currents and electrical fields.
Zone LPZ 1 is the first zone within the building and prone to the induced
fields and flashover into the building.
Zone LPZ 2 is the second zone within the building where the risk to
electrical equipment is still high.
Zone LPZ 3 is the third zone and subsequent areas of diminishing risk
to the equipment.
SPD Selection
In the main distribution board and as close to the service entrance as
possible, this will probably only be possible after the meter.
Structural Lightning Protection System (LPS) installed (or overhead
mains supply) a Type 1 device is fitted typical to PD Devices’
T1SP3/25/100/230 for critical buildings i.e. hospitals, schools, etc. For
less critical buildings T1SP3/12.5/50/230 are recommended. Single
phase versions are also available.
Structural Lightning Protection System (LPS) and metal services
installed a Type 1 device similar to the PD Devices’ Enhanced DSP
Series can be utilised. Although these are of a lower current impulse,
they offer an all mode protection.
Without a structural LPS fitted and underground mains supply feed
a Type 2 device is fitted similar to the PD Devices’ DSP Series or SPM
series. The T1SP Series devices would offer the same levels of protection.
Critical Equipment – Here it is advisable to install Type 3 devices to
ensure the protection level is kept to below the recommended 1500 volt.
The PD Devices’ DSP Series being Type 2 and 3 can be fitted. In cases
where the protection needs to be at the equipment itself, then devices
similar to the PD Devices’ MBP type of products are advisable.
Telecommunication and Data Equipment should be protected by
additional devices similar to PD Devices’ TLP and DBP ranges. The panel
is the best place for surge protection when dealing with transient
overvoltages. There are many reasons for this:
• Multiple circuits can be protected by one device, rather than the
multiple ‘at equipment’ devices that would otherwise be required
• Limits the electromagnetic propagation of the overvoltage. Surge
protection in the panel limits the inductive coupling to other
conductors by minimising the size of the conducting ‘loop’ (e.g. phase
to earth) during an overvoltage event
• Electrically ‘noisy’ equipment is usually supplied by its own ring or
spur, so a surge protection device in the panel is effectively between
the ‘noisy’ source and the equipment that requires protection
• Maintenance and monitoring of the surge protection is centralised
and simplified, as many panel products have options for automatic
monitoring and pre-failure warning
• As panels are normally located at the entrance to an installation or
area, the installation of surge protection at the panel fits well with the
Lightning Protection Zone concept of BS EN 62305
• Lead lengths can be controlled and kept to a minimum, loops can be
eliminated
• Ensures a good co-ordinated approach