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Generator bay, not just a protection relay

A generator bay requires safe connection of the generator to the busbars or grid, machine protection, voltage and frequency monitoring, breaker control, and communication with SCADA, DCS or PMS systems. Customers rarely ask for an "87G relay" in isolation, they need a complete bay function.

SYMAP® is configured for this application according to the generator type, CT/VT measurements, synchronization needs, differential protection, grid-code requirements, number of DI/DO signals and communication architecture.

Motor bay in an industrial substation

One platform, configuration based on the application

SYMAP® has a broad base function package for generator bays. With SYMAP® Compact+ GC, configuration includes hardware options (3×I, 9×U, Ig, Ug, DI/DO, communication modules) and software/application options in the Order Code; advanced functions such as 87G differential protection, distance 21, synchronization 25A or EZA controller are selected as separate items. With the classical SYMAP® series (G, BCG/ECG), available functions follow from the chosen hardware and variant configuration.

When a function is available in the chosen configuration, it can be used concurrently with all other available functions, with no limit on the number of active protections, protection "points" or simultaneous use.

Just describe the generator type and connection point, we will propose the appropriate SYMAP® configuration through hardware, variant and options.

Typical generator applications

Six most common scenarios where SYMAP® generator protection is applied

Diesel gensets

Industrial, marine and mobile diesel gensets for standby or continuous power. Safe connection, reverse power, loss of excitation and synchronization.

Gas engines and CHP

Cogeneration gas engines, biogas plants. Grid-code requirements, reactive power regulation, parallel operation with the distribution grid.

Hydropower plants

Small and micro hydropower plants (up to ~10 MW). Grid synchronization, 87G generator protection per machine size, frequency and voltage regulation.

Marine generators

Main and auxiliary diesel gensets on ships and offshore platforms. Classification approval (DNV, BV, LR, ABS), PMS integration.

DP vessels and offshore

Multiple redundant generator groups, coordination with DP/IAS systems, fast load shedding logic and blackout prevention.

Standby generators

Data centers, hospitals, industrial plants with critical loads. ATS coordination, black-start, periodic test operation.

Relevant protection functions

The list is limited to functions typically present in a generator application. SYMAP® series covers more than 40 ANSI functions; the full overview is in the technical catalog.

The Status column indicates how the function is obtained in the configuration. The status legend is below the table.

Function ANSI Status Brief description
Overcurrent and short-circuit protection 50, 51 AVAILABLE CONDITION Base function on CT inputs. IDMT characteristics per project coordination with the generator feeder.
Ground fault protection 50N/51N, 59N AVAILABLE CONDITION Depends on Ig or Ug measurement and the way the generator star point is grounded.
Reverse power 32 AVAILABLE Protects the prime mover from motoring effect; trips when power flows from the grid into the generator.
Loss of excitation / reactive power 40Q AVAILABLE Detects loss of the excitation system; prevents asynchronous operation and generator damage.
Voltage and frequency protection 27/59/81 AVAILABLE CONDITION Generator VT required. Setpoints per grid-code requirements or classification standards.
Synchronization and sync-check 25 / 25A OPTION CONDITION Generator VT + bus/grid VT mandatory. 25A automatic synchronization is a Compact+ SW option or a classical SYMAP® G variant.
Generator differential protection 87G OPTION CONDITION Compact+ SW option or a dedicated variant. Additional CT inputs on the generator neutral side.
Distance protection 21 OPTION Optional when the generator bay also handles line/grid protection (less common).

Function status legend:

AVAILABLE IN PLATFORMFunction is part of the wide functional package of the SYMAP / Compact+ platform. Configured per project, not a separate relay. MEASURING / SIGNAL CONDITIONFunction is available but requires the appropriate CT, VT/PT, Ig, Ug, DI/DO, trip-circuit wiring or communication signal. OPTION / VARIANTFunction requires an Order Code option, a specific variant, additional CT groups, communication channel or project configuration.

Compact+ or classic SYMAP®?

Compact+ GC is a Protection & Control IED for a single generation unit connecting to the grid, EZA/EZE, Grid Code, NA protection, sync-check. For multi-generator Power Management (parallel operation, load sharing, automatic load shedding, bus-tie logic, diesel genset control), classic SYMAP® Y-G for stand-alone or SYMAP® BCG / ECG for full PMS remains the choice.

What SYMAP® requires as input

Configuration starts from the available CT/VT inputs and synchronization requirements, not from variant selection

Measurements
  • Current: 3×CT on the generator feeder for all generator protections. Additional CT on the neutral side for 87G if required.
  • Ground fault: Ig measurement (CBCT) or residual summation of phase CTs; depends on the star-point grounding.
  • FEEDER group (generator voltage): 3×U on the generator feeder for 27/59/81, 32, 40 and synchronization. Part of the base configuration.
  • BUS1 / BUS2 group (reference voltage): 3×U on the busbars or grid side for sync-check 25 and grid-code functions. BUS1 is part of the base configuration; BUS2 is added for multi-busbar arrangements.
  • Auxiliary signals: Bearing and winding temperatures (RTD), AVR and governor parameters, monitoring of auxiliary systems.
Signals and outputs
  • Digital inputs (DI): Generator breaker status, AVR, governor, local/remote mode, sync request.
  • Relay outputs (DO): Breaker trip, close commands, AVR/governor signals for synchronization, alarms and interlocks.
  • High-speed output: Trip contact with guaranteed operating time for 87G, 32, 40 and fast grid-code functions.
  • Analog outputs: 4–20 mA for P, Q, U, f, cosφ values to SCADA/PMS systems.
  • Communication: IEC 61850/GOOSE, Modbus TCP/RTU, IEC 60870-5-104, PROFIBUS DP per architecture.

Recommended SYMAP® configurations

Four levels of complexity, plus retrofit. Selected based on generator size, connection type, and 87G requirement.

Generator with grid synchronization
SYMAP® Compact+ GC

Typical application: Generator + grid + synchronization in a single device. Typical for CHP plants, biogas, smaller hydro up to ~10 MW.

Hardware: 3×I + Ig + 9×U + Ug, DI/DO.

Typical selection: Compact+ GC sa 25A i EZA-controller OPTION.

Stand-alone generator protection
SYMAP® Y-G

Typical application: Classical generator protection for stand-alone applications. For modular SYMAP® Y/BC architectures.

Hardware: 3×I + Ig + 3×U for 27/59/81/32/40.

Sync-check 25 available as a base function; 25A automatic as a VARIANT.

Marine, offshore and island PMS
SYMAP® BCG (MV) or ECG (LV)

Typical application: Marine, offshore and island systems with multiple generators and PMS functions.

Hardware: dedicated variant with relay-to-relay communication for load sharing.

Typical selection: BCG (MV) or ECG (LV) by busbar location.

Large generators with 87G differential
SYMAP® Y-G (87G variant) or Compact+ +F1-+GC

Typical application: Large and critical generators (above ~2 MW). 87G protects the generator winding against internal faults.

Status: OPTION (Compact+) or a dedicated SYMAP® Y-G variant (✓3,4 in Y matrix).

Hardware: additional CT inputs on the generator neutral side.

Not sure which configuration fits?

Send the generator parameters, single-line diagram and grid-code requirements. We will propose the appropriate SYMAP® configuration.

Technical proposal

Questions that shape the configuration

Send this information together with the single-line diagram; we will propose the appropriate SYMAP® configuration

  1. What is the generator rated power? Power, voltage and rated current determine CT ratios, protection thresholds and the need for 87G.
  2. Synchronization with the grid, with a busbar, or with another generator? The synchronization type defines the number of voltage systems and whether 25A automatic synchronization is needed.
  3. Is 87G generator differential protection required? A Compact+ SW option or a classical SYMAP® G/BCG variant. Requires additional CT inputs on the neutral side.
  4. What is the point of connection (MV, LV, HV)? Determines the VT voltage range and the relevant grid-code reference.
  5. Is there a grid-code requirement (G99, VDE-AR-N 4110/4120, EZA/EZE)? Drives the choice of Compact+ GC with EZA controller and required certification.
  6. What is the communication interface to PMS/SCADA/DCS? IEC 61850/GOOSE, Modbus TCP/RTU, IEC 60870-5-104, PROFIBUS DP.
  7. Marine or offshore classification (DNV, BV, LR, ABS, RINA)? Drives the need for certified devices and specific variants.
  8. New installation or retrofit? Retrofit defines mechanical and electrical constraints based on the existing scheme and HIMAP legacy.
Control and interlocking
  • Breaker or contactor control
  • Local and remote modes with acknowledgment
  • Start/stop logic with condition checks
  • Interlocking with adjacent drives
  • Start block based on thermal image
Communication and SCADA/DCS
  • IEC 61850 Ed. 1 and Ed. 2, GOOSE
  • Modbus RTU and Modbus TCP
  • IEC 60870-5-103 and IEC 60870-5-104
  • PROFIBUS DP (optional)
  • RSTP, HSR, PRP (IEC 62439-3)
Diagnostics and maintenance
  • Event recorder and fault records
  • Disturbance recorder, COMTRADE
  • Self-diagnostics and watchdog mechanisms
  • Counters for starts, running hours and trips
  • Support for FAT and SAT, commissioning

SYMAP® products for generator applications

This application page links to the product pages where full technical specifications are available

SYMAP® Compact+ GC

Generator & Grid Controller, protection, grid monitoring and grid-code control in a single device. 25A, EZA controller, G59/G99 options.

Open page →
SYMAP® series (G / BCG / ECG)

Classical generator variants for stand-alone applications and PMS systems with multiple generators.

Open page →

Next step

Send the generator parameters, single-line diagram, grid-code requirements and synchronization type. We will propose the appropriate SYMAP® configuration, ANSI functions, settings ranges and Order Code.

Technical proposal Compact+ GC Order Code Technical inquiry

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