MiCOM P12x Relay: P120, P121, P122, P123, P126, P127

Short answer

The Schneider Electric MiCOM P12x relays (P120, P121, P122, P123, P125, P126 and P127) are phase and earth overcurrent relays for feeders, transformers and medium-voltage backup. They are very common in installed switchgear. Schneider now lists the range as being phased out, with end-of-sale and end-of-service dates published per model.

What it is and where it is used

The MiCOM P12x relay is Schneider Electric’s compact overcurrent family. It includes the P120, P121, P122, P123, P125, P126 and P127, and the self-powered or basic-input P111 and P115. It is one of the most widely installed relays in medium-voltage switchgear: feeders, distribution transformers, small motors and backup of high-voltage bays. For the general context, see protective relays.

Variants: P120, P121, P122, P123, P125, P126 and P127

Model	Application	Main difference
P111 / P115	Simple distribution switchgear	Basic overcurrent; the P115 can be self-powered from the CTs
P120	Earth or single phase	Single-input overcurrent
P121	Basic feeders	Non-directional phase and earth
P122	Feeders and transformers	More stages, thermal image and additional functions
P123	Overhead feeders	As the P122, with auto-reclosing and more inputs and outputs
P125	Networks with directional earth fault	Directional earth fault with residual voltage input
P126	Feeders with directional earth fault	Phase, directional earth fault and auto-reclosing
P127	Feeders with generation or rings	Directional with voltage inputs: voltage, frequency and power

What changes from one model to another

Schneider Electric’s range page describes the P12x series as directional and non-directional overcurrent relays, from the single-phase or earth-fault unit up to the P127, which is three-phase and has voltage functions. The manual for the P125, P126 and P127 (the AREVA version, now mirrored in third-party repositories) allows more detail:

Directional and wattmetric earth fault (32N / IeCos): present in all three models, with broken-conductor detection. This is what allows them to be applied on isolated or compensated neutral networks, where a plain earth overcurrent relay does not discriminate well.
Three-phase overcurrent, directional or not (67/50/51): only in the P126 and P127. These two models add undercurrent (37), negative sequence (46), thermal image (49), residual overvoltage (59N) and auto-reclosing of up to four shots (79).
Voltage (27/59): only the P127.
Others: breaker failure (50BF), cold load pickup, switch-onto-fault (SOTF), logic selectivity between relays and programmable logic with AND gates. There are two setting groups.
Inputs and outputs: the manual lists 4 logic inputs on the P125 and 7 on the P126 and P127, with 5 and 8 output relays respectively; relay RL1 is the trip relay.

The current inputs accept 1 A or 5 A CTs, with the value defined in the settings. Earth sensitivity is divided into three ranges (high, medium and low) according to the earth current range. When replacing a relay, therefore, confirm that the selected range matches the installed core-balance CT.

Hardware and communications

According to the official page, the case is 4U, 20 TE or 30 TE, and fully withdrawable. It has a wide-range auxiliary supply (24 to 250 Vdc / 48 to 240 Vac). Its rear RS485 port supports the Modbus, IEC 60870-5-103, DNP3 and Courier protocols, depending on the model ordered. The manual also lists a front RS232 port for setting from a PC. The setting software of the AREVA era was called MiCOM S1. In the sources we consulted, P12x communication is serial only: when a substation migrates to IEC 61850, these relays are integrated through a gateway or replaced. To go further: ABB SPAJ, SPAM and REF54x legacy relays.

Life cycle

Schneider currently lists the P12x range as being phased out. We have not found an official successor for each model in the sources consulted; the closest family in the company’s current offering is Easergy P3, which does have Ethernet and IEC 61850. The equivalence must be defined case by case, because case dimensions, wiring and logic change.

Common mistakes

Replacing a P126 with a P125 when ordering a spare: without three-phase directional overcurrent, the feeder would end up with less protection than designed.
Leaving the earth sensitivity range wrong: with a core-balance CT and a low range, the relay never picks up on resistive faults.
Reversing the polarity of the residual voltage or of the earth current: the directional earth fault and wattmetric elements give the opposite direction, and the relay trips for external faults or fails to trip for its own.

Main functions

Function	ANSI	What it provides
Phase and earth overcurrent	50/51, 50N/51N	Main protection (guide)
Directional earth fault (P125, P126) and directional phase (P127)	67N, 67	Selectivity in rings (directional elements)
Auto-reclosing (P123, P126, P127)	79	Overhead networks (guide)
Thermal image	49	Overload (guide)
Unbalance and broken conductor	46	Open phase (guide)
Breaker failure	50BF	Local backup
Voltage and frequency (P127)	27, 59, 81	Abnormal conditions and connected generation

Communications and integration

MiCOM P12x relays communicate mainly through the rear serial port using Modbus, IEC 60870-5-103 or DNP3, depending on the model. To bring them into a modern SCADA system, a gateway is usually used. Configuration, settings and the download of events and oscillography are done with Easergy Studio (formerly MiCOM S1 Studio). To go further: MiCOM P139 sheet and feeder settings.

In many panels the P12x relays coexist with larger MiCOM relays, such as the MiCOM P14x, and with equipment from other brands; coordination between them is checked in the protection study.

Frequently asked technical questions

Which manual applies to the MiCOM P123? Schneider publishes the technical manual per range and version; use the one for your relay’s version.
Easergy Studio does not connect: it is usually the port, the baud rate or a missing data model.
Trips when energizing transformers: inrush current can make the instantaneous element operate; see overcurrent trip on start-up or energization.
Forgotten password: it is recovered with the manufacturer’s procedure, not by forcing the device.

If your relay is no longer manufactured

Schneider Electric lists the P12x range as being phased out, with end-of-sale and end-of-service dates per model. Its current line of compact medium-voltage relays is Easergy P3 (which Schneider also presents as PowerLogic P3). Migrating means translating settings and logic, reviewing wiring and communications, and testing the new relay; we do it through remote configuration, retrofit design and testing.

How we help

At Tiza Group we configure and review MiCOM P12x relays remotely with Easergy Studio, worldwide, based on the coordination study and the approved settings, and we configure the relay that replaces them. See remote configuration of Schneider Electric Easergy and MiCOM relays. If your P123 tripped and the reason is not clear, we will quote the trip analysis. For the replacement, we do the design under engineering design and studies. Write to us through the contact page.

References

IEEE C37.2, device function numbers.
IEC 60870-5-103.
Schneider Electric, MiCOM P120 to P127 range (status and documents) and the P127 product sheet with life-cycle dates.

Frequently asked questions

What is the difference between the MiCOM P122, P123 and P127?

All three are phase and earth overcurrent relays. The P122 and P123 are non-directional, and the P123 adds functions such as auto-reclosing; the P127 is directional for phase and earth faults and has voltage inputs, with voltage, frequency and power functions. The exact model and its options are read from the ordering code.

Which software configures a MiCOM P123?

Schneider Electric's Easergy Studio, the tool formerly called MiCOM S1 Studio. You need to install the data model that matches the relay's model and version.

Is the MiCOM P127 still manufactured?

Schneider Electric lists the P12x range as being phased out. For a P127 it publishes end of commercialization on 31 December 2029 and end of service on 31 December 2034. Check the date for your exact model and plan the replacement well in advance.