ANSI device numbers protection

ANSI device numbers, defined by the IEEE C37.2 standard, provide a system of 99 numeric identifiers to designate protection, control, and switching functions in electric power systems. Their application is universal in single-line diagrams, substation plans, and relay schematics, enabling precise technical communication in the field of electrical engineering.

List of ANSI device numbers (IEEE C37.2)

The following table lists 69 device numbers and subnumbers used in electrical system protection, according to ANSI/IEEE C37.2-2008 nomenclature.

ANSI Number	Designation
1	Main element (Master Element)
2	Time delay starting or closing relay
3	Verification or interlocking relay, complete sequence
4	Main protection relay
5	Stopping device – emergency stop switch
6	Automatic starting switch
7	Rate of change relay
7F	Rate of change of frequency relay (ROCOF)
8	Control power disconnecting device
9	Reversing device
10	Unit sequence switch
11	Multifunction device
12	Overspeed device
13	Synchronous speed device
14	Underspeed device
15	Speed or frequency matching device
16	Data communications device
17	Shunt or discharge switch
18	Acceleration or deceleration device
19	Starting-to-running transition contactor
20	Electrically operated valve (solenoid valve)
21	Distance relay
21G	Ground distance
21P	Phase-to-phase distance
22	Equalizer circuit breaker
23	Temperature control device, heater
24	Volts per hertz relay (V/Hz)
25	Synchronizing or synchronism check device
26	Apparatus thermal device, temperature switch
27	Undervoltage relay
27P	Phase undervoltage
27S	DC undervoltage relay
27TN	Neutral undervoltage by third harmonic
27TN/59N	100% stator ground fault protection
27X	Auxiliary undervoltage
27 AUX	Auxiliary undervoltage input
27/27X	Bus/line undervoltage
27/50	Inadvertent energization
28	Flame detector
29	Isolating contactor
30	Annunciator relay
31	Separate excitation device
32	Directional power relay
32L	Low forward power
32H	High directional power
32N	Wattmetric zero-sequence directional
32P	Directional power
32R	Reverse power
33	Position switch
34	Master sequence device
35	Brush operating or slip-ring shorting device
36	Polarity or polarizing voltage device
37	Undercurrent or underpower relay
37P	Underpower
38	Bearing protection device / Bearing RTD
39	Mechanical condition monitor (vibration)
40	Field relay / loss of excitation
41	Field circuit breaker
42	Running circuit breaker
43	Manual transfer or selector device
44	Unit sequence starting relay
45	Atmospheric condition monitor (smoke, fire)
46	Reverse-phase or stator current unbalance relay
47	Phase-sequence or voltage unbalance relay
48	Incomplete sequence relay / locked rotor
49	Machine or transformer thermal relay / thermal overload
49RTD	RTD-compensated thermal overload
50	Instantaneous overcurrent relay
50BF	Breaker failure or local backup (LBB)
50DD	Current disturbance detector
50EF	End fault protection
50G	Instantaneous ground overcurrent
50IG	Instantaneous isolated ground overcurrent
50LR	Acceleration time
50N	Instantaneous neutral overcurrent
50NBF	Instantaneous neutral breaker failure
50P	Instantaneous phase overcurrent
50SG	Instantaneous sensitive ground overcurrent
50SP	Split-phase instantaneous current
50Q	Instantaneous negative-sequence overcurrent
50/27	Inadvertent energization
50/51	Instantaneous/timed overcurrent relay
50/74	Current transformer (CT) failure
50/87	Instantaneous differential
51	AC time overcurrent relay
51C	Voltage-controlled time overcurrent
51G	Time ground overcurrent
51LR	Locked rotor time overcurrent protection
51N	Time neutral overcurrent
51P	Time phase overcurrent
51R	Locked/stalled rotor
51V	Voltage-restrained time overcurrent
51Q	Time negative-sequence overcurrent
52	AC circuit breaker
52a	Switch position contact (open when switch is open)
52b	Switch position contact (closed when switch is open)
53	Exciter or DC generator relay
54	Turning gear device
55	Power factor relay
56	Field application relay
57	Short-circuit or grounding device
58	Rectification failure relay
59	Overvoltage relay
59B	Bank phase overvoltage
59N	Neutral overvoltage
59NU	Neutral voltage unbalance
59P	Phase overvoltage
59X	Auxiliary overvoltage
59Q	Negative-sequence overvoltage
60	Voltage or current balance relay
60N	Neutral current unbalance
60P	Phase current unbalance
61	Density switch or sensor
62	Time delay stopping or opening relay
63	Pressure detector (pressure switch)
64	Ground protection relay
64F	Field ground protection
64R	Rotor ground fault
64REF	Restricted earth fault differential
64S	Stator ground fault
64TN	100% stator ground
65	Speed governor
66	Notching device / maximum starts, starts per hour, or time between starts
67	AC directional overcurrent relay
67G	Directional ground overcurrent
67N	Directional neutral overcurrent
67Ns	Directional ground fault
67P	Directional phase overcurrent
67SG	Directional sensitive ground overcurrent
67Q	Directional negative-sequence overcurrent
68	Blocking relay / power swing blocking
69	Permissive control device

Frequently Asked Questions (FAQ)

What is an ANSI device number in electrical protection?

An ANSI device number is a standardized numeric code that identifies a protection, control, or supervision function in electrical equipment, according to the IEEE C37.2 standard. Each number represents a specific operation, for example, 50 corresponds to instantaneous overcurrent and 51 to time overcurrent.

What is the difference between number 50 and number 51?

Number 50 designates an instantaneous overcurrent protection, which operates without intentional delay when the current exceeds the set threshold. Number 51 indicates a time overcurrent protection, whose trip time is inversely proportional to the current magnitude (inverse time curve) or defined by a fixed delay.

Can multiple ANSI numbers be combined in the same relay?

Yes, it is a common practice in modern numerical relays (IEDs). A single device can implement multiple functions indicated by numbers separated by a slash, such as 50/51 (instantaneous and time overcurrent) or 67/67N (directional phase and neutral), which is reflected in single-line diagrams.

Which ANSI number protects against ground faults in the stator of a generator?

The most commonly used functions are 64S (stator ground fault), 64TN (100% stator protection), and 27TN/59N, which monitors third harmonic voltage and residual voltage to detect faults along the entire winding length.

How is a number like 50/87 interpreted in a protection scheme?

The notation 50/87 combines the instantaneous overcurrent function (50) with instantaneous differential protection (87). It is generally used for schemes where an instantaneous overcurrent element backs up the main differential protection, ensuring fast tripping for internal faults.

Where is number 87 typically applied?

Number 87 corresponds to differential protection. It is applied in power transformers (87T), generators (87G), buses (87B), and transmission lines (87L), comparing currents entering and leaving the protected zone to detect internal faults with high sensitivity.

References

• engineeringtoolbox.com: https://www.engineeringtoolbox.com/isa-intrumentation-codes-d_415.html