SERVICE AND PRODUCTS FOR ELECTRIC UTILITIES
Subject: Transformer Suggested Specification
M-3311A Suggested Spec 120610
Protection, metering, and monitoring for 2/3/4 winding transformers shall be provided by a microprocessor-based package. The microprocessor-based package shall be suitable for any transformer and CT winding configuration. The relay shall include extensive self-testing and alarm output contacts for indication of self-test warning, failure conditions, or removal of input power.
The relay shall include the following protection functions, features, and options:
Overexcitation Protection (24): Optional
The F24 function shall have a definite time setting and at least 4 families of Inverse Time Curves to provide protection of over-excitation condition.
Undervoltage Protection (27): Optional
The F27 function for undervoltage and/or load shedding shall include an undervoltage inhibit feature to disable the undervoltage function for voltages below the inhibit set point to prevent misoperation during fault conditions.
Negative Sequence Overcurrent (46)
The F46 function shall have Definite Time and Inverse Time characteristic for detection of open conductors and for increased sensitivity for phase to phase fault backup feeder protection. Eight time overcurrent curves including the IEC Inverse, Very Inverse, Extremely Inverse, and Long Time Inverse curves shall be included.
Winding Thermal Protection (49)
The F46 winding thermal protection curve shall be based on the IEC-255-8 standard and provide protection against possible damage during overload conditions.
Breaker Failure Protection (50BF/50NBF)
The breaker failure shall include a phase overcurrent detector (50BF) for breaker failure detection and a neutral overcurrent detector (50BFN) to provide protection for breaker flashover each associated transformer winding.
Instantaneous and Time Phase Overcurrent Protection (50/51)
The relay shall include a 50/51 phase instantaneous and time overcurrent functions for each associated transformer winding. The F50 phase instantaneous overcurrent function shall provide fast tripping for high fault currents. The F51 phase time overcurrent function shall provide selective time coordination protection with down stream devices. Eleven time overcurrent curves including the IEC Inverse, Very Inverse, Extremely Inverse, and Long Time Inverse curves and the IEEE Moderately Inverse, Very Inverse, and Extremely Inverse curves shall be included. A 50/51 function shall be provided for each associated transformer winding.
Instantaneous and Time Neutral Overcurrent Protection (50N/51N)
The relay shall include a 50N/51N neutral instantaneous and time overcurrent functions for each associated transformer winding. The F50N neutral instantaneous overcurrent function shall provide fast tripping for high fault currents. The F51N Residual time overcurrent function shall provide sensitive ground fault protection. Eleven time overcurrent curves including the IEC Inverse, Very Inverse, Extremely Inverse, and Long Time Inverse curves and the IEEE Moderately Inverse, Very Inverse, and Extremely Inverse curves shall be included. A 50N/51N function shall be provided for each associated transformer winding.
Instantaneous and Time Ground Overcurrent Protection (50G/51G)
The relay shall include at least two 50G/51G instantaneous and time ground overcurrent functions. The F50G/F51G overcurrent functions shall provide sensitive and selective coordination with up stream or downstream breakers. Eleven time overcurrent curves including the IEC Inverse, Very Inverse, Extremely Inverse, and Long Time Inverse curves and the IEEE Moderately Inverse, Very Inverse, and Extremely Inverse curves shall be included.
Over / Under Frequency (81O/81U): Optional
The relay shall include at least 4 set points for over / under frequency operation for use in load shedding applications. The frequency functions shall be automatically disabled when the voltage falls below the measurable range.
Ground Differential (Restricted Earth Fault) Protection (87GD)
The relay shall include at least one 87GD for two winding, two 87GD for three winding and three 87GD functions for four winding application. The 87GD function should use existing phase differential and ground CTs eliminating the need for dedicated CTs. To obtain additional security for CT ratio errors and saturation during external faults, 87GD function shall use a directional element based on product (-3Io x Ig cos Ø) to distinguish between internal and external faults. To provide fast operation for internal ground faults with the load breaker open, the directional element shall adaptively change to non-directional when the calculated zero-sequence current from the phase CTs is very small (such as 140ma for 5A rated CT).
Phase Differential Function (87T)
The 87T function shall employ a dual slope harmonic restraint characteristic. To prevent misoperation on low levels of 2nd harmonic for transformer inrush current, the 87T function should utilize both 2nd and 4th harmonic restraint to prevent misoperation during transformer energization. Cross phase averaging option shall be available to accommodate point on wave switching if required.
The 87T shall use an adaptive 5th harmonic restraint pickup level during system overexcitation conditions. The increase in 5th harmonic should not be used to block the differential element (87T) during this condition which will delay tripping. The increase in 5th harmonic shall be used to automatically increase the 87T minimum pickup level to a higher user selectable value.
High Set Phase Differential Function (87H)
The relay should include an unrestrained high set phase differential element 87H function for close-in fault protection.
Programmable Logic
The relay shall include user programmable logic permitting custom creation of logic with relay functions, inputs, outputs, and time delay. The logic shall be created by simple option selection on display screen graphics. Programming in mathematical equations shall not be required.
Through-Fault Monitor Event Log
The relay shall have Through Fault Recorder, which records Through Faults. Each through fault record shall contains the serial number of the fault, duration of the event, maximum RMS fault current magnitude for each phase during the fault, I2t and the time stamp of the fault. In addition, it shall also store the total number of through faults since last reset, and total I2t for each phase since last reset. The relay shall have the memory to store a total of 256 or more through faults.
Breaker Monitoring
The Breaker Monitoring function calculates an estimate of the per-phase wear on the breaker contacts by measuring and integrating the current (selected as I2t or It) passing through the breaker contacts during the interruption interval. The per-phase values are summed as an accumulated total for each phase, and then compared to a user-programmed threshold value. When the threshold is exceeded in any phase, the relay can activate a programmable output contact. The accumulated value for each phase can be displayed as an actual value.
Transformer Winding & CT Connection Configuration
The relay shall accommodate all ANSI/IEEE and IEC transformer winding and CT connection configurations. These configurations shall be easily selected from pop-down menus. The relay shall internally compensate for the various CT and transformer winding configurations. When delta-connected CTs are used, the relay shall allow the 50, 51 and 46 functions to be set in terms of line current quantities, and the metering status screen shall correctly displays the line currents, not delta currents.
Custom Transformer Winding & CT Connection Configuration
The relay shall be able to accommodate advanced applications such as a wye-delta transformer with a zero sequence source (grounding transformer) inside the zone of protection of the delta winding. For this application, the standard zero sequence elimination on the wye winding can be turned off ensuring correct 87T differential operation.
Overcurrent Summing
The relay 50/50N and 51/51N overcurrent functions and the 87GD ground differential functions should be able to accommodate current summing for breaker and half and ring bus applications.
Configuration Matrix
The relay shall provide a graphical display of the programmed inputs and outputs for each function. The display matrix shall be hyperlinked to each function setting element allowing elements to be turned on and off for testing purposes. To ensure all function outputs are re-enabled after testing has been completed; the matrix display shall provide visual identification of function outputs that have been temporary disabled.
Metering / Commissioning Display Tools
For metering purposes and to assist in commissioning, the relay shall provide a graphical display of the following quantities;
· Phase currents for each transformer winding
· Positive , negative, and zero sequence currents for each transformer winding
· Fundamental restraint currents for each phase
· Fundamental differential currents for each phase
· Second, fourth, and fifth harmonic currents for each phase
The relay shall provide graphical display of uncompensated and compensated phasors for commissioning and wiring verification purposes.
The relay shall provide real time metering of voltage, three-phase and neutral currents, real time demand with user selectable intervals of 15, 30, or 60 minutes, and maximum demand with date and time stamp.
Metering accuracies shall be at least:
· Voltage: ± 0.5 V or ± 0.5%, whichever is greater (range 0 to 180V ac)
· Current: 5 A rating, ± 0.1 A or ± 3%, whichever is greater (range 0 to 14 A)
· 1 A rating, ± 0.02 A or ± 3%, whichever is greater (0 to 2.8 A)
· Frequency: ± 0.10 Hz (from 57 to 63 Hz for 60 Hz models; from 47 to 53 Hz for 50 Hz models)
Access/Communications/Integration Capabilities
The relay shall provide access via a front-panel HMI. The following communication ports shall be provided:
· Two RS-232 serial ports, one located on the front of the relay for local communication via a laptop, and one located on the rear of the relay for remote communication.
· One isolated RS-485 serial port on the rear of the relay for remote communication.
· RS-232 and RS-485 shall support Modbus® and DNP communication protocols.
· One IRIG-B port.
Tripped Function Status Indication and Target Log Capabilities
The relay shall display tripped function status on the front of HMI. The relay shall also have the option of being supplied with a Target Module Display that will indicate tripped function status by LED’s. The relay shall provide a target log for each trip operation that includes the function(s) operated, the functions picked up, input/output status, time stamp, and phase and neutral currents at the time of trip. A total of at least 10 target logs shall be stored in a first in, first out buffer, with the oldest records being automatically overwritten.
Sequence of Events Log
The relay shall store the Sequence of Events Log records all status information and all parameters measured or calculated by the relay when triggered by selectable relay events. The Sequence of Events Log shall include 512 or more of the most recently recorded relay events. The triggering of the event recorder shall be user selectable from a user-friendly table containing pickup, trip and dropout of all elements and IPSLogic® results, and pickup and dropout of all inputs and outputs. All events time stamped to 1 ms resolution.
Waveform Capture Capabilities
An oscillograph recorder shall provide comprehensive data recording of all monitored waveforms, and the status of inputs and outputs, storing up to 152 cycles of data. The total record length is user-configurable for up to 4 partitions. The sampling rate shall be at least 16 times the power system nominal frequency (50 or 60 Hz). The recorder shall be capable of being triggered by either designated status inputs, trip outputs, or via serial communications or from the optional front panel HMI. The recorder shall continuously store waveform data, keeping the most recent data in memory. When triggered, the recorder shall continue to store data in memory for a user-defined, post-trigger delay period. Records may be stored in COMTRADE format.
User Software for Interface and Analysis
User interface software shall be provided that is menu-driven and Windows based. Using the software, the user shall be able to: view setpoints, set elements, configure the elements, configure the trip/block matrix, create programmable logic schemes, view metering, view the target log, view the event log,
download the oscillograph files, load files from a PC to the relay, load files from the relay to the PC, and print all settings.
Waveform (oscillograph) viewing software shall be provided that can open, view and be used for analysis of captured waveforms. Graphical display of the analog voltage and current traces, as well as the status of the inputs and outputs will be viewable. In addition, harmonics and RMS values may be viewed. Analysis tools such as phasor diagrams, R-X diagrams and P-Q diagrams will be available. Zooming abilities, curser manipulation with attendant value display, and multiple cursor difference quantities shall be provided. Power factor and frequency traces will also be viewable.
Communications protocols
The relay shall provide DNP 3.0 and MODBUS protocols. The relay shall have the option to provide DNP 3.0 over TCP/IP and MODBUS over TCP/IP through an RJ45 Ethernet port.
Time sysnchronization
The relay shall have IRIG-B Time Synchronization with 1 ms resolution time stamp on recorded events and oscillography.
I/O Count and Description
The following I/O shall be provided:
· Control/Status Inputs – 6 dry type contact inputs, (24V dc internally wetted)
· For applications requiring externally wetted contact inputs, optional interface device shall be available that can interface external voltages from 9V to 320V dc.
· Contact Outputs – 8 outputs; 6 form “a”, and 2 form “c”.
· Fixed Power Supply failure alarm output contact; 1 form “a”.
· Fixed Self-Test failure alarm output contact; 1 form “c”.
Expanded I/O Count and Description
The relay shall be capable of having additional I/O provided:
· Additional Control/Status Inputs – 12 dry type contact inputs, (24V dc internally wetted)
· Additional Contact Outputs – 8 outputs; form “a”.
Power supply requirements
The relay shall be capable of having a redundant power supply as an option. The redundant power supply shall be on hot standby to prevent power interruption to the relay during failure of one of the power supplies or sources. The relay shall have independent sets of terminals for each power source, so that they can be connected through redundant cables and fuses to independent batteries and/or ac power sources to keep the protective relay operational during a battery/ac power source failure.
The relay shall accommodate redundant power supplies with different voltage ranges:
High voltage: Shall operate properly from 80 V dc to 312.5 V dc or 85 V ac to 265 V ac, and shall withstand 315 V dc or 300 V ac for 1 sec.