As someone who has been dealing with substations and power equipment for a long time, when choosing a relay protection testing instrument, the core factor is: it must precisely match the type of protection you want to test and also be compatible with the voltage level at the site. There is no need to pursue “the most comprehensive functions”, but it must be “adequate, easy to use, and in line with standards”. The three-phase, six-phase, and microcomputer relay protection testers that are often heard about in the market can easily cause confusion. In fact, the essential differences lie in two points – the number of output channels is different, and the corresponding application scenarios are also different. Choosing the right one can save a lot of detours and also save costs; choosing the wrong one, either the complex protection cannot be tested, or the unnecessary functions purchased are useless.
Based on years of on-site operation and testing experience, from the four aspects of “how to distinguish models”, “how to choose correctly”, “which one should be used in different scenarios”, and “which standards must be met”, I will explain the selection process in detail for everyone. There are no professional terms piled up, only practical干货.
1. Core distinction： Three-phase， six-phase， microcomputer， how to distinguish?
When we select equipment on-site， we don’t need to worry about the term “microcomputer”， the key is to look at “three-phase” and “six-phase”， because microcomputer is the current mainstream architecture， most three-phase and six-phase devices belong to microcomputer relay protection instruments， only with differences in functions and channels.
1. Three-phase relay protection tester (commonly used， cost-effective choice)
Its core configuration is 3 channels of voltage + 3 channels of current， the function is relatively basic， but sufficient to handle our daily routine tests. For example， when testing line protection， overcurrent relays， undervoltage relays， as well as reclosing， backup auto-switching， these common protection devices， it is completely fine to use it.
The 35kV and below substations that I maintain most of the time mostly use three-phase equipment， the operation is simple， the volume is not large， it is convenient to carry， and the price is relatively affordable. For scenarios with limited budgets and simple testing needs (such as small factories， rural power grid operation， school teaching)， three-phase equipment is recommended， it can fully meet the needs of daily maintenance and setting value verification， without spending extra money on more complex models.
2. Six-phase relay protection tester (essential for complex scenarios， one-stop choice)
It has twice the channels of the three-phase equipment， that is， 6 channels of voltage + 6 channels of current. The core advantage is “multiple channels independent output” – this point is extremely important for testing complex protection. For example， when testing transformer differential protection or busbar differential protection， we need to simulate different fault states on the high and low voltage sides of the transformer， if using three-phase equipment， we have to repeatedly disconnect and connect wires， simulate in multiple steps， which is not only time-consuming and laborious， but also prone to errors； but using six-phase equipment， we can complete the simulation at once， significantly improving the testing efficiency， and ensuring the accuracy of the test results.
If the maintenance is for substations of 110kV and above， or when testing main transformers and busbar differential protection frequently， it is recommended to directly choose six-phase equipment， although the price is a little higher， it can save a lot of subsequent manpower and time costs， and it can also be downward compatible with all functions of three-phase equipment， making it easier to expand testing scenarios in the future without having to purchase again.
3. Microcomputer relay protection tester (not the “third type of model”， but the mainstream architecture)
Many people will list it together with three-phase and six-phase， but that’s not the case – the mainstream relay protection testers on the market are basically microcomputer relay protection instruments. Its core is “industrial computer + DSP architecture”， characterized by high precision， comprehensive functions， and programmability， capable of completing various complex tests such as setting value verification， action time testing， harmonic testing， etc.
In simple terms， the three-phase or six-phase equipment we choose， as long as it is produced in recent years， is basically a microcomputer relay protection instrument； the confusion we have about “choosing three-phase or six-phase” is essentially choosing the number of channels， while “microcomputer” is just the basic architecture of the equipment， not an independent selection dimension， the key is still to see if the channels and functions match your own needs. II. Practical Selection: Find the Right Scenario, No More Confusion
Many people get confused by various parameters when choosing a model. In fact, as long as you identify your “usage scenario”, you can quickly determine the appropriate model without having to repeatedly consult and compare parameters, saving time and effort.
The basic entry-level model is suitable for simple verification scenarios and is mainly used for single types of relays and old protection devices. It does not require complex tests and the output channels are mostly single-phase or 3V + 3A as the basic configuration. It adopts a single-chip microcomputer architecture, is simple to operate and inexpensive, with a precision of 0.2 grade (error 0.2%). Its core functions include setting value verification and action time testing, suitable for scenarios with limited budgets such as teaching, small factory maintenance, and simple rural network maintenance. This type of equipment is relatively large in size and is more suitable for fixed-site use.
The mainstream practical model is suitable for conventional substations and is compatible with microcomputer protection for 110kV and below conventional substations. It is mainly used for daily operation and maintenance, and the output channels can be flexibly selected as 3V + 3A or 6V + 6A according to the type of protection. It adopts an industrial control computer + true DSP architecture, with a precision of 0.1 grade (error 0.1%), and has functions such as status sequence, harmonic test, distance protection, and differential protection, capable of meeting the requirements of complex tests. The equipment weighs moderately and is portable, suitable for on-site operation in substations.
The high-end professional model is suitable for intelligent and ultra-high voltage substations and is compatible with 220kV and above intelligent substations and new energy power stations (photovoltaic/wind power). The output channels are 6V + 6A or digital analog integration, supporting optical fiber digital communication, and adopts an industrial control computer + DSP architecture. It supports IEC 61850 (essential for intelligent stations) with a precision of 0.05 grade (high precision) and has microsecond-level synchronization capabilities. Its core functions include optical fiber digital communication (GOOSE/SV), fault playback, transient simulation, etc. It is mainly lightweight and handheld, with a built-in battery, suitable for outdoor and high-altitude on-site debugging.
A practical suggestion: If the main maintenance is for conventional substations and the tests usually include line protection, overcurrent protection, reclosing verification, etc., choose three-phase equipment that complies with the 2010 version specifications, which is cost-effective and sufficient. If in the future, you need to connect to intelligent substations or ultra-high voltage projects, or frequently test main transformer differential protection, busbar differential protection, generator-transformer group protection, etc., it is recommended to directly choose equipment that complies with the 2023 version specifications and supports IEC 61850 to avoid additional costs due to later upgrades.
III. Application Scope: Match Exactly, No Mistakes or Waste
Based on our actual on-site usage scenarios, let’s clarify the applicable scope of each model to avoid situations where “the equipment is not used” or “it is insufficient”. Precise matching of requirements is the most cost-effective approach.
1. Three-phase equipment: Recommended for basic needs, the best value for money
Mainly applicable to substations of 35kV and below, such as those in rural areas and small factories. The testing requirements are mainly line protection, overcurrent protection, reclosing verification, and occasionally testing undervoltage relays. Three-phase equipment is sufficient for these tasks. Additionally, schools for teaching and internal primary maintenance of enterprises can also choose three-phase equipment, which is simple to operate, inexpensive, and can meet basic teaching and maintenance needs without pursuing high-end models.
2. Six-phase equipment: Essential for complex protection, compatible with all basic scenarios
Mainly applicable to substations of 110kV and above, especially for scenarios that require testing transformer differential protection, busbar differential protection, generator-transformer group protection – these complex protections require multiple currents to be input for calculation. The multi-channel advantage of the six-phase equipment can be fully utilized, eliminating the need to repeatedly connect and disconnect wires, significantly improving on-site testing efficiency. Moreover, it can be fully compatible with all functions of three-phase equipment, even when testing conventional protection, using six-phase equipment is still fine, suitable for scenarios with comprehensive requirements and long-term expansion needs. 3. Microcomputer Relay Protection Instrument: Covers All Scenarios, Mainstream Must Be Selected
As mentioned earlier, the microcomputer relay protection instrument is not a “third type of machine”, but the current mainstream architecture. Whether it is three-phase or six-phase, as long as it is produced in recent years, it is basically a microcomputer relay protection instrument. Its application scope covers all the above scenarios, from basic teaching and simple maintenance, to routine substation operation and maintenance, and to intelligent station debugging. It can meet all requirements, except for the difference in the number of channels and expansion functions – therefore, when we make the selection, we focus on the channels and functions, and don’t worry about whether it is a microcomputer or not, because there are basically no non-microcomputer relay protection instruments anymore.
4. Standard Regulations: Relationship with Test Results’ Authority and Equipment Compliance
As power industry practitioners, we all know that equipment must comply with national standards and industry norms; otherwise, the test results are invalid and there may be potential safety hazards. No matter which relay protection instrument is selected, the following standards must be met. During procurement, it is necessary to clearly specify the requirements to avoid purchasing outdated models that do not comply with the norms.
1. Manufacturing Standards (The equipment itself must comply)
GB/T 7261-2016 “Basic Test Methods for Relay Protection and Safety Automatic Devices”: This is the most basic test method standard. All relay protection instruments must comply with it, which is equivalent to the “entry threshold” of the equipment. Without meeting this standard, the equipment cannot be used for on-site testing.
DL/T 624-2010 “Technical Conditions for Microcomputer Relay Protection Test Devices”: This is the core industry standard for microcomputer relay protection instruments in China. The mainstream equipment on the market basically follows this standard. Additionally, the new version (draft for approval in 2023) has been implemented, with higher requirements for the equipment’s accuracy and transient performance. If there is a long-term usage requirement, it is recommended to prioritize selecting equipment that complies with the 2023 version of the standard to avoid being eliminated in the future.
2. Measurement and Calibration Standards (The equipment must be regularly calibrated)
JJG 1112-2015 “Relay Protection Test Instrument”: This is the national measurement calibration regulation. In simple terms, the relay protection instrument we purchase must be sent to a professional institution for calibration once a year to ensure that its output accuracy meets the requirements. Otherwise, the test results will not be authoritative and may even cause protection device malfunctions, leading to safety accidents. During procurement, it is necessary to confirm that the equipment supports calibration in accordance with this regulation to avoid being unable to calibrate in the future.
3. On-site Test Procedures (On-site testing must be followed)
DL/T 995-2016 “Inspection Procedures for Relay Protection and Grid Safety Automatic Devices”: This is a guiding document for on-site testing. It clearly defines the test items, test methods, and qualification criteria for different protection devices. The selected relay protection instrument must meet the test requirements in this regulation. Otherwise, it cannot complete the on-site inspection work.
Here is a reminder: Technical specifications are constantly updated (from version 1997 to 2010, and then to 2023 version). The requirements for accuracy and functionality are getting higher and higher. During procurement, it is necessary to ask clearly which version of the specification the equipment complies with. It is recommended to prioritize selecting the 2010 version and above, and definitely do not buy outdated models designed based on outdated specifications to avoid being unable to meet the on-site testing requirements in the future and causing waste.
Finally, here is a small suggestion for you: If you can clearly define your specific test object (such as mainly testing line protection or transformer differential protection), the voltage level at the site (10kV/35kV/110kV/220kV), and even the budget range, you can further narrow the selection range and directly lock in the most suitable model without worrying about the numerous parameters and models.
Post time: Apr-13-2026