Genset surge protection is the coordinated set of surge protective devices, bonding conductors and discharge paths that stand between a lightning strike or a switching event and the alternator, the AVR and every control board wired to the genset. A board that only carries devices on the mains side leaves the alternator feeding its own controls through an unprotected path. Yangzhou Tesla Power Equipment Co., Ltd. fits the devices, the bonding and the labels before the canopy closes, so the board that lands on site matches the single-line diagram priced in the offer. The layout is decided on the drawing before the set is built, not after a board fails on site. This guide explains how the protection zones map onto a generator board, which SPD classes sit where, how the earth path is sized, and which records prove the work at handover. Send your single-line diagram to our quotation desk and the SPD schedule comes back beside the genset price.
- Class I: takes the direct-strike share at the service entrance, beside the genset main breaker.
- Class II: takes the switching and induced share at the sub-boards that feed the AVR and the controller.
- Bonding: the discharge path is only as good as its length; half a metre of lead adds roughly a kilovolt.
- Records: every device lands on the single-line diagram and in the test record before shipment.
What Does Genset Surge Protection Cover on an Export Set?
The phrase covers three circuits that share one board. The power circuit runs from the alternator terminals through the main breaker to the outgoing feed, and a direct or induced impulse rides it at line voltage. The control circuit runs from the controller to the AVR, the battery charger and the transfer panel, and those electronics fail at a fraction of the voltage the power circuit shrugs off. The earthing circuit ties both to the earth bar, and it carries the impulse away only while every bond stays short.
Buyers comparing genset surge protection manufacturers should ask which of the three circuits the quoted devices actually cover. A quote that protects the outgoing feed but leaves the controller across an unbonded gap protects the load and not the set. Ask for the board drawing with the devices marked on it, and ask which protection zone each device serves. The answers separate a board built for export duty from one built to pass a glance.
How Do SPD Classes Split the Duty on a Generator Board?
The classes divide the work by waveform and by position. A Class I device handles the 10/350 waveform of a partial direct strike, so it belongs at the service entrance where that impulse first lands. A Class II device handles the 8/20 waveform of induced and switching events, so it belongs at the sub-boards that feed the AVR, the controller and the chargers. A Class III device adds a final trim at the socket that feeds fine electronics. Stacking Class II devices alone is a common quote that leaves the entrance undefended.
The split matters most on boards for critical duty. The 1000kW hospital container build carries both classes at the entrance because the controller cannot restart a hospital bus alone after a board fault. Ask any tender for the class and the position of every device. Two Class II devices at the entrance do less than one Class I device there, and the difference shows up on the worst day of the year.
Which Surge Numbers Belong on the Generator Datasheet?
Three figures carry the specification. The nominal discharge current says how much impulse the device repeats without dying, and the waveform beside it says which test proved that. The voltage protection level says how far the residual voltage climbs, and the lead length turns that figure into the number the equipment actually sees. The maximum continuous operating voltage says how high the board can sit in steady state before the device starts to leak. Quotes that arrive from genset surge protection suppliers in China often name the class but omit the waveform, and the omission hides the weakest of the three.
Put the three figures on the datasheet beside the generator ratings, and the board becomes checkable. An inspector reads the device marking, compares it with the datasheet and signs. Without them the same inspector records a black block with two cables and an opinion. The device families listed in the IEC publications index carry the test sequences behind the markings, and the marking only means something beside the datasheet line that quotes it. Tesla Power prints the waveform, the In and the Up beside the class on every export datasheet.
| SPD class | Where it sits | Discharge current In | Protection level Up | Duty it takes |
|---|---|---|---|---|
| Class I | Service entrance, beside the genset main breaker | 12.5kA to 25kA (10/350) | 2.5kV or lower | Direct-strike share |
| Class II | Sub-boards feeding AVR, controller, chargers | 20kA to 40kA (8/20) | 1.5kV or lower | Switching and induced share |
| Class III | Socket outlets feeding fine electronics | 6kA to 10kA (8/20) | 1.2kV or lower | Residual inside the room |
| Class I+II combined | Compact boards with one entrance bay | 12.5kA plus 20kA | 2.5kV or lower | Both shares, one device |
What Does the Sizing Arithmetic Look Like on a 400kVA Set?
Run the arithmetic before the board is signed off. A 400kVA set at 0.8 power factor delivers 400kVA x 0.8 = 320kW of real power, and the full-load current at 400 V works out to about 577 A. A Class I device with In of 12.5kA and an Up of 1.5kV sits half a metre from the breaker, so the lead adds roughly 1kV and the equipment sees up to 2.5kV. The alternator winding and the AVR front end tolerate more than that, so the layout holds. The same check on a lead of 2m pushes the residual past 3.5kV and the layout no longer holds. Tesla Power marks both the device and the lead length on the drawing.
A genset for telecom huts repeats the same check with a smaller frame. A 100kVA tower set at 0.8 power factor delivers 100kVA x 0.8 = 80kW, and the current at 400 V works out to about 144 A. A Class II device with In of 20kA and an Up of 1.2kV sits beside the rectifier board, the lead adds 0.5kV, and the rectifier sees up to 1.7kV. The rating definitions behind both checks sit in the 2018 edition of ISO 8528-1, which is also where a buyer checks the duty class the set was offered against. A set offered at a standby rating with a prime duty load carries more heat and more switching events than the nameplate suggests, and the devices age faster.
What Earthing Arrangement Keeps the Discharge Path Short?
The discharge path is geometry before it is electronics. Every metre of lead between the device and the earth bar adds roughly a kilovolt to the residual voltage, so a correctly rated device on a careless lead protects nothing. Bolt the Class I device to the busbar it guards. Land the earth bar on the foundation earth with the shortest bond the pit allows. Keep the controller earth off the power earth run and tie both at one point, so the impulse does not use the control cable as its way home.
Site practice decides the rest. A pit in rock, a high-resistance soil and a canopy bolted to a skid all change the picture, so the arrangement belongs on the drawing with the bolt sizes written in. The notes in the site preparation guide cover the pit detail for poor ground. Test the bond at commissioning with a micro-ohmmeter and write the reading in the record, because a bond that measures 2 ohms today will carry the full impulse badly in year three.
How Should Surge Protection Appear in the Handover File?
The handover file turns the board into something a service team can maintain. It should carry the single-line diagram with every device marked, the datasheet for each device with its class, waveform and protection level, and the commissioning bond readings taken on the day. Photograph the board with the canopy open before it ships, so the device positions are provable if the file and the hardware ever disagree. Tesla Power Equipment staples that set into the same folder as the engine records, because the two fail audits for the same reason. The practice holds for any genset for construction site duty, where the board rides on a skid and the bonds take trailer shock every move.
Documentation written for export buyers should also name the replacement part numbers, so a site team orders the right card instead of a lookalike. Buyers who need a template can copy the layout used on a hospital handover: diagram, datasheets, bond readings, photographs and a signed surge record page, in that order. Conformity assessment for the EU market references the same documents, and an inspector who finds them in ten minutes signs in ten minutes.
When Does a Transfer Switch Need Its Own Surge Attention?
The transfer panel sees the event from both sides. It sits between two live sources, and a switching transient at the moment of transfer lands on coils and control cards built for steady duty. Give the panel its own Class II devices on the control supply, keep its control wiring out of the same tray as the power run, and bond its enclosure to the same earth bar as the board. The monthly inspection cycle in the NFPA 110 chapter on transfer assumes the panel survives the switching event it performs, and the assumption only holds when the bonding holds.
Watch the open-transition panels first. They break the load before they make it, and the interruption itself is a small surge event on the control side at every transfer. A panel that transfers cleanly with short bonds and a protected control supply outlives the set around it. A panel that chatters after a storm is telling the site team which tray the impulse used.
Which Site Conditions Push the Surge Risk Up?
Geography writes the first line of the risk. Coastal plains, river valleys and isolated towers take more strikes than a city block, and a set on high ground collects what the plain misses. Thin soil raises the earth resistance and stretches the discharge path, so the same device works harder for the same result. High sites add the derating question: the figures in the high site derating note belong beside the SPD schedule, because a derated set carries a different current and the protective settings move with it.
Load side writes the second line. A board feeding VSDs, UPS rectifiers and soft starters generates its own switching events every hour, and the Class II devices at those sub-boards age on switching rather than on lightning. Ask for the device count per board in the offer, and treat a single device at the entrance as a quote for a quiet site. Tesla Power sizes the count from the load schedule, not from the frame size, and the same question put to any bidder returns a better board.
How Do You Upgrade an Ageing Board Without a Full Rewire?
Upgrade in three moves. First, fit a combined Class I+II device at the entrance if the bay allows one, and re-bond it with a lead shorter than the one it replaces. Second, add Class II devices at the sub-boards that feed the AVR, the charger and the transfer panel, and photograph the result for the file. Third, replace any device whose window shows black or whose flag has tripped, and log the date. The 500kVA canopy set with the ATS option takes all three moves in a single service visit.
Sequence the work against the service calendar rather than the storm season. A board opened for devices in the dry month retests calmly, and the bond readings go into the file with the rest of the annual records. Buyers planning an upgrade can ask for surge protection supplier quotations to be itemised line by line, so the devices, the bonds and the labour price separately and the comparison stays honest. The same three moves serve a genset for farm irrigation duty, where the board sits outdoors and the storm season sets the calendar for everyone.
Frequently asked questions about genset surge protection
Yes. The AVR regulates steady-state voltage; it cannot clip an impulse that rises and falls inside a microsecond. Surge protection for generator boards starts where the AVR ends, and the two are specified together so the regulation band and the protection level do not overlap.
The names follow the test waveform. Type 1 devices are tested with the 10/350 waveform of a partial direct strike and sit at the entrance. Type 2 devices are tested with the 8/20 waveform of induced and switching events and sit at the sub-boards. A board normally carries both, and the datasheet states which test each device passed; Tesla Power lists the device makes per class in the offer.
As close to the equipment they guard as the geometry allows. Generator surge protection for data centres usually starts at the sub-board that feeds the UPS input, because that board sees both the mains events and the switching events of the rectifier front end. The entrance device catches the strike share; the sub-board devices catch what remains.
Inspect visually at every service and read the status flags; most devices declare their own end of life. Replace on the flag, after any known nearby strike, and on the schedule the maker states. Tesla Power ships the replacement cards in the commissioning spares kit, so the first replacement needs no shipment from the factory.
A machine warranty covers the machine as built, so surge damage on an unprotected board sits outside it, while damage on a board built to the specification is a claim against the build. Buyers who specify surge protection for hospital sites ask for the device makes in the warranty annex, which keeps the claim and the hardware in the same document.
Rarely. One entrance device catches the direct share and leaves the sub-boards to catch what remains, and the residual voltage at a long lead reaches the controls anyway. Zoned protection costs less than the first controller it saves, and the zones are already drawn on the single-line diagram.
Diagram, datasheets, bond readings, photographs and the signed surge record. The surge record page lists each device, its marking, the reading taken on commissioning day and the date, so the next service visit starts from evidence rather than from memory. File it with the engine records and the audit takes minutes. Tesla Power files the same pack on every export order.