Protection and control
Protection relays
Numerical relays that measure currents and voltages from instrument transformers and trip the breaker when the scheme's conditions are met.
At a glance
- Standard
- IEC 60255 seriesmeasuring relays and protection equipment
- Inputs
- current and voltage transformersratios and classes set by the scheme
- Functions
- overcurrent, earth fault, differential and moreset by the protected equipment
- Communication
- protocol set by the substation system
- Settings
- applied at commissioningagreed with the network operator where required
A protection relay is specified by the equipment it protects and the scheme it sits in. A feeder relay commonly provides overcurrent and earth fault protection. A transformer relay adds differential protection. A motor relay adds thermal and starting supervision. The functions are often referred to by their ANSI device numbers, for example 50 and 51 for overcurrent and 87 for differential protection.
The relay depends on what feeds it. The current and voltage transformer ratios and classes, the auxiliary supply voltage and the communication protocol of the substation system all have to match, and settings are calculated from the network study and applied at commissioning.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Protected equipment | Feeder, transformer, motor, generator, busbar | The single line diagram |
| Protection functions | Overcurrent, earth fault, differential, voltage, frequency | The protection scheme |
| Current and voltage inputs | 1 A or 5 A secondary, voltage inputs | The instrument transformers |
| Auxiliary supply | DC or AC voltage | The station battery or auxiliary system |
| Communication | Substation protocol and ports | The control system |
| Mounting | Flush panel mounting, cut out size | The panel, especially for replacements |
| Inputs and outputs | Number of binary inputs and output contacts | Interlocking and alarm needs |
Typical options are the ones buyers most often specify. They are not a list of what is available, which is confirmed per enquiry.
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 60255-1 | Measuring relays and protection equipment, common requirements |
| IEC 60255 series | Functional and product requirements for protection relays |
The standard that applies is set by the specification and the destination market. Editions change, so the edition cited in a specification is confirmed in the quotation.
Documents normally requested
| Document | What it evidences |
|---|---|
| Technical datasheet | Ratings, functions and the variant offered |
| Type test report or certificate | The design has passed the tests of its standard |
| Dimensional drawing | Mounting, cut out and connection positions |
| Wiring or connection diagram | Terminals, auxiliary supply and communication |
| Settings and configuration files | Where a device is supplied preconfigured |
| Manual | Installation, commissioning and operation |
Where a device replaces an existing one, the nameplate, model and firmware of the existing device are the most useful documents to send.
What we need to quote accurately
| 01 | Device type and the system voltage it serves |
| 02 | Rated current and the short circuit breaking or withstand values required |
| 03 | The protection scheme and functions needed, and the scheme it must integrate with |
| 04 | Auxiliary supply voltage and communication protocol |
| 05 | Whether this replaces an existing device, with its nameplate or model if known |
| 06 | Quantity, destination, required delivery date and acceptable condition |
| 07 | Current and voltage transformer ratios, and the secondary current rating |
| 08 | The communication protocol of the substation system |
Delivery and logistics
Devices are lighter to move than transformers and switchboards, but compatibility is the harder part of the delivery. A replacement breaker has to fit the existing panel, a relay has to fit the cut out and the scheme, and a firmware or communication mismatch can make a correct device unusable on the day.
Delivery dates are stated in each quotation for the specific item offered. We do not publish a general lead time.
Common questions
Do you calculate protection settings?
No. Settings come from the network study and are applied by the party that commissions the scheme. We source relays specified to carry the functions and interfaces the scheme needs.
Related
Request a quote for this equipment
Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.