Type a device number (27, 50/51, 87G) or a line from a relay or a drawing. Each number gets its own card.
A whole line can be pasted, such as "Relay: 50/51, 27/59, 32R" or "protection 50/51N 46 49": the page finds the numbers in it. Values with units (50 Hz, 400 A) and CT ratios are left out.
Enter the device function numbers from a protection relay, a generator protection unit or a switchboard drawing: 27, 32, 50/51, 27/59, 51N, 87G, 81O/81U, or a whole line such as "protection 50/51N 46 49". The page says in plain words what each number and each letter after it means, reads a combined form part by part and, where two sources agree, gives the IEC symbol. The request line can be copied or added to the RFQ.
Only what two independent sources give the same way is decoded; anything else is marked as not decoded. There are no settings, no trip values and no choice of protections here: the relay manual and the drawing govern.
The number, from 1 to 99 in IEEE C37.2, names the function of a device: 27 undervoltage, 50 instantaneous overcurrent, 51 time overcurrent, 87 differential. A stroke joins the functions of one device: 50/51, 27/59. Numbers 97 to 99 are left for uses specific to an installation.
A letter after the number narrows the function: N neutral, G ground or generator, P phase, T transformer, M motor, B bus, L line, O and U over and under, BF breaker failure. Some lettered forms have a meaning of their own: 32R reverse power, 51V voltage-restrained overcurrent, 81R rate of change of frequency.
IEC names functions by symbols instead of numbers: U< undervoltage, U> overvoltage, f> and f< over and under frequency, I2> negative-sequence current. A symbol is given only where two sources agree; for 50 and 51 the sources pair the stages I>, I>> and I>>> differently, so none is given.
| Number | Name | IEC symbol | Example |
|---|---|---|---|
| 21 | Distance relay | — | 21 |
| 24 | Volts per hertz relay | — | 24 |
| 25 | Synchronizing or synchronism-check device | — | 25 |
| 27 | Undervoltage relay | U< | 27 |
| 32 | Directional power relay; 32R reverse power | — | 32R |
| 37 | Undercurrent or underpower relay | — | 37 |
| 40 | Field relay (loss of excitation) | — | 40 |
| 46 | Reverse-phase or phase-balance current relay | I2> | 46 |
| 47 | Phase-sequence or phase-balance voltage relay | U2> | 47 |
| 49 | Machine or transformer thermal relay | — | 49 |
| 50 | Instantaneous overcurrent relay; 50BF breaker failure | Sources differ | 50BF |
| 51 | AC time overcurrent relay; 51N neutral, 51V voltage-restrained | Sources differ | 51V |
| 52 | AC circuit breaker | — | 52 |
| 59 | Overvoltage relay; 59N neutral overvoltage | U>; U0> for 59N | 59N |
| 64 | Ground detector relay; 64F field, 64S stator | — | 64S |
| 67 | AC directional overcurrent relay; 67N neutral | — | 67N |
| 79 | AC reclosing relay | — | 79 |
| 81 | Frequency relay; 81O over, 81U under, 81R rate of change | f> for 81O, f< for 81U | 81O/81U |
| 86 | Lockout relay | — | 86 |
| 87 | Differential protective relay; 87G generator, 87T transformer, 87B bus | — | 87G |
The page decodes every example in this table the same way. The IEC symbol is given where two sources name the same one; a dash means none is given here.
Device names: the IEEE C37.2 list from a relay maker device number chart and an automation maker data sheet with the full definitions, checked against a reference encyclopedia and an electrical engineering notes site. Letters and lettered forms: the same chart and data sheet, the notes site and a protection relay code chart. IEC symbols: the notes site, the automation maker data sheet and a relay maker data sheet. Left out: number 7 (the sources differ), numbers 95 and 96 (named in one list, left for specific applications in others), 64R (written both for the rotor and for restricted earth fault), single letters with several meanings (A, C, F, H, Q, R, S, V on their own), a lower case a or b after a number (auxiliary contacts) and lettered forms with one source; IEC symbols for 50 and 51, which the sources pair with the overcurrent stages differently.
50 is the instantaneous overcurrent function: it acts with no intentional time delay when the current rises above a set value. 51 is the AC time overcurrent function: it acts after a time delay that depends on the current. Written 50/51, the two functions sit in one device.
N stands for neutral: the element works on the neutral or residual current or voltage, as in 51N or 59N. G stands for ground (earth) or for generator, and the standard gives both: 51G is a ground time overcurrent element, while 87G is generator differential protection. The relay manual or the drawing says which applies.
32 is the directional power relay, which acts on power flowing in a set direction. 32R is reverse power: power flowing the wrong way, for example from the system into a generator.
81 is the frequency relay. O stands for over and U for under, so 81O acts on over frequency and 81U on under frequency. 81R acts on the rate of change of frequency.
No. It reads the meaning of the numbers and letters printed on a relay or a drawing. Which functions are fitted and how they are set comes from the relay manual and the drawings of the installation.
A number or a letter is decoded only where two independent sources give it the same meaning. Numbers 7, 95 and 96, single letters with several meanings and lettered forms with one source are left out. IEEE C37.2 device numbers run from 1 to 99, so a larger figure is not decoded here: the drawing legend explains it.
A decoded number is a cross-check, not a choice of protection. Attach a photograph of the relay front or its rating plate and the drawing page, and Vessel Core checks the numbers before an offer goes back.
