PROTECTION SYSTEMS
HARDWARE IN THE LOOP TESTING

The RTDS Simulator offers the most advanced and effective means available for testing protection systems. Since the simulation runs in real time, the physical protection equipment can be connected in closed-loop with the power system model.

The controlled and flexible environment of the digital simulation allows protection equipment to be subjected to virtually all possible faults and operating conditions. The closed-loop interaction of the protection system with the network model provides insight on both the performance of the relay scheme as well as its effect on the power system.

As is illustrated below, a model of the power system is implemented on the RTDS Simulator that includes the high voltage components (e.g. lines, breakers, instrument transformers, power transformers, generators, etc.) plus the required protection and control functions not included in the equipment under test.

 

Testing via Electrical Interface

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Typically, detailed models of the instrument transformers (CT, PT and CVTs) are used to provide signals to digital to analogue (D/A) converters. These signals are proportional to the secondary voltage and current signals the protection equipment would see in service. Including the instrument transformers in the model makes it possible to evaluate their effect on the performance of the protection system. Alternatively the primary voltage and current signals can be sent directly to the protection equipment using the appropriate scaling factor.

The analogue output of the RTDS Simulator is provided by the GTAO card, which utilizes 16-bit D/A converters and allows high accuracy gain and offset calibration. The GTAO operates over a maximum range of +/- 10 Vpeak. To provide secondary voltage and current to the protection equipment, the GTAO output is connected to power amplifiers. In some cases, however, the GTAO output is connected directly to the protection equipment for “low level” testing, which bypasses the auxiliary current and voltage transformers inside the protection equipment.

 

Testing via IEC 61850 Interface

When testing IEC 61850-9-2 or IEC 61869-9 Sampled Value (SV) compliant devices, the GTAO and power amplifiers can be replaced by the GTNETx2 card, running the SV network protocol. The GTFPGA Unit can also be configured to stream IEC 61850-9-2LE or IEC 61869-9 Sampled Values by using the GTFPGA-SV component and firmware.

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With the secondary voltage and current provided to the protection equipment via GTAO and power amplifiers or the GTNET-SV or GTFPGA-SV, the protection will respond as though connected in the actual network. The protection should respond to faults by providing trip and possibly subsequent reclose signals. Since the network model is simulated in real time, the signals from the protection will be used to operate breakers modeled in the simulation. The breaker models can include the mechanical operating time (either fixed or statistically varied) and provide breaker status.

There are several ways for the breaker commands to be imported into the real time simulation from the protection equipment. If the protection provides signals via conventional dry contacts they can be input either via a Low Voltage Digital Input/Output Interface Panel, which is included with the RTDS cubicle (no additional hardware is needed), or a GTDI card. Dry contacts can be connected directly to the inputs of the Low Voltage Digital Interface panel, but must be “wetted” using a voltage source when connected to the current driven input of the GTDI card. An appropriate current limiting resistor, dependent on the voltage level, must be used when connecting wetted contacts to the GTDI card.

If the protection equipment is IEC 61850 compliant, the breaker commands can be imported into the simulation using the GTNET-GSE firmware. The GTNET-GSE supports both GOOSE and GSSE (UCA GOOSE) messaging.

The breaker commands available in the RTDS Simulator are used to open and close the breakers (3 pole or single-pole). Depending on the type of protection being tested, it may be necessary to send the breaker status out of the Simulator to the protection equipment. Breaker status can be provided to conventional relays using the 250 Vdc Digital Output Interface Panel which includes dry contacts controlled by the simulation. The dry contacts included on the 250 Vdc Digital Output Interface Panel are solid state devices that operate in less than 0.2 ms and can accommodate any voltage level to a maximum of 250 Vdc. The 250 Vdc Digital Output Interface Panel is an additional piece of hardware that can be outfitted on the Simulator cubicle if desired.

Again, if the protection equipment is IEC 61850 compliant, the breaker status can be exported from the simulation using the GTNET-GSE.

Binary communication between protection equipment (e.g. POTT) can be transferred through the RTDS Simulator so that the signal delay can be included in testing. Therefore, coordinated protection schemes can be tested using the RTDS Simulator to observe interaction between the components of the protection system (e.g. between different relays) and between the protection and the power system.

With the real time simulation and the protection equipment connected in closed-loop, the protection device can be subjected to a myriad of faults and operating scenarios. Each condition can easily be repeated to investigate misoperations or test the equipment stability.

The faults and operating scenarios can be run manually from the RunTime console or using the automated batch mode facility. The automated batch mode facility is often applied to protection system testing where faults are repeated again and again with small changes to the fault inception angle, fault type, fault location, etc. These cases can all be run automatically controlled by C-type Script implemented with the automated batch mode facility. Scripts can even record, store, print and evaluate results. The results can be saved in RSCAD MultiPlot, COMTRADE, jpg or pdf format. Key data from results (trip times, max/min values, etc.) can be stored in ASCII or MS Word report files.

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