Point-to-point testing verifies, signal by signal, that every status, alarm, measurement and control in the signal list travels its whole path correctly: from the contact or instrument transformer in the switchyard, through the IED and the gateway, to the substation HMI and the control center. The value, the text, the protocol address, the quality and the time stamp are checked and, for controls, that they operate the right device.
What point-to-point testing is
In a substation, every breaker status, alarm, measurement and control is a signal that travels a chain: it starts at an auxiliary contact or an instrument transformer, enters an IED (relay or bay controller), travels over the substation network, reaches the local HMI and, through the gateway, the control center. Point-to-point testing checks that whole chain, signal by signal.
It is also called signal commissioning or, when it covers the full substation automation system (SAS), SAS point-to-point checks. In the process industry, IEC 62382 covers the electrical and instrumentation loop check, which is the same idea applied to instruments and control systems. In substations, the reference is the substation signal list: the test consists of proving that every row of that list works.
The path of a signal
- 01Source in the switchyardAuxiliary contact, equipment alarm, CT or VT
- 02Bay IEDBinary or analog input, text and time stamp
- 03Substation HMIDisplay, alarm, event and log
- 04GatewayProtocol address toward the control center
- 05Control centerValue, quality and control back
Each leg can fail for different reasons: a wire on the wrong terminal, an input misconfigured in the IED, a misspelled text in the HMI, a crossed address in the gateway or an object mismapped in the control center database.
What is checked by signal type
| Signal type | What is checked |
|---|---|
| Double-point status (breaker, disconnect switch) | Open, closed and, where applicable, the intermediate or invalid state; text and color in the HMI |
| Alarm or single-point status | Activation and reset, priority and text in the HMI and in the control center |
| Analog measurement | Value at several points of the scale, unit, deadband and power sign |
| Control | That the command from each level opens or closes the right device and respects interlocks and the local/remote selector |
| Counter or energy | Increment and consistency with the meter |
| Protection events | Pickups and trips with their time stamp and the right sequence |
Quality and time stamp. Besides the value, each signal carries quality attributes (valid, substituted, test, blocked) and a time stamp. The test confirms that the time stamp is created at the source and not at the gateway, and that all devices share the same time.
Controls. Controls are always tested with the real equipment and with the installation in a safe condition. Select-before-operate, rejection when an interlock is not met and the response when the selector is in local are all verified; see select before operate (SBO).
In an IEC 61850 substation
With IEC 61850, much of the wiring between devices is replaced by messages. The position of a disconnect switch can travel by GOOSE to another bay for an interlock, and the HMI reads it over MMS as an attribute of a logical node. Point-to-point testing grows: besides the terminal-to-IED leg, each data item is checked to be correctly published and subscribed according to the substation configuration file, and IEDs in test mode must flag their data with the matching quality so nobody takes it as real. Before the test it is worth reviewing the SCD file; you can open it with our free IEC 61850 SCL viewer.
Where it fits in commissioning
Point-to-point testing is usually done in two parts:
- From the switchyard to the HMI. During the SAT of each bay, with the signals produced at their source: operating the equipment, simulating the alarm at the terminal or injecting the quantity. This is the part that uncovers wiring errors.
- From the HMI to the control center. With the local system already tested, each protocol address is verified with the control center, often by forcing values from the IED or the database so that switching does not have to be repeated.
If the factory acceptance test (FAT) of the panels was complete, the first leg on site focuses on field wiring. In industry, signals from the MCCs to the DCS are tested the same way, as described in commissioning electrical panels and MCCs. It is one of the stages of substation commissioning.
Errors the test finds
- Inverted statuses: the HMI shows closed when the breaker is open, because an a contact was wired as b.
- Measurements with the wrong CT or VT ratio configured, or with the power sign reversed.
- Protocol addresses crossed between bays in the gateway, so the control center operates the wrong device. The topic is explained in IEC 61850 mapping to IEC 104 and DNP3.
- Time stamps generated at the gateway, which scramble the sequence of events.
- Alarm texts and priorities different from the approved ones.
What is delivered
The signed-off signal list, with one check box per leg (IED, HMI, gateway, control center), the result of each signal, the nonconformities and their closure. That list is part of the commissioning dossier and is the basis for any future modification and for maintenance testing. The exact test procedure of a project depends on its signal list, its protocol and the control center requirements.
Signals and SCADA with Tiza Group
If the problem lies in the configuration of the IEDs or the gateway, we start with remote relay configuration, which also covers control and communications, worldwide. On site, our crew performs point-to-point testing with the control center in medium, high and extra-high voltage substations and in industry, in Colombia, or elsewhere on request. Contact us.
Related guides
- Substation signal list for SCADA
- Interlocking tests
- SCADA, SAS, DCS and HMI: differences in the power sector
- IEC 61850 mapping to IEC 104 and DNP3
- Commissioning levels: from FAT to integrated systems testing
References
- IEC 62382:2024, Control systems in the process industry – Electrical and instrumentation loop check.
- IEC 60870-5-104: telecontrol over TCP/IP, data types and causes of transmission.
- IEEE 1815 (DNP3).
- IEC TR 61850-90-2:2016: using IEC 61850 between substations and control centers.
- IEC 61850-7-4: logical node classes.
- CIGRE TB 637, Acceptance, commissioning and field testing techniques for protection and automation systems, 2015.
Frequently asked questions
What is point-to-point testing in a substation?
It is the individual verification of each signal in the signal list along its whole path, from the switchyard equipment to the HMI and the control center. The real signal is produced at its source and confirmed to arrive at each destination with the right text, value, quality and time stamp.
Can point-to-point testing use simulation instead of the real signal?
Partly. The test from the gateway to the control center is usually done by forcing values from the IED or the database. But the first leg, from the equipment terminal to the IED, must be tested with the real or injected signal at its source, because that is where wiring errors appear.
Who takes part in point-to-point testing with the control center?
The test crew at the substation, the control system integrator and the operators of the control center that receives the signals. When the asset is supervised from the utility's or system operator's control center, the test is coordinated with them under their procedures.