Tātaitai IDMT grading
Whakatakotoria ngā kōpiko tuku o ngā relay overcurrent wā-whakahuri.
Reads IEC 60255-151:2009 / IEEE C37.112-2018. Tables checked 26 Sept 2026.
Whakamātau mahi 6
Ka whakakī ia mahi i ngā uara tauira. Whakakapia ērā ki ō uara.
- Grade two relaysThe operating times of a feeder and an incomer relay at 4 kA.
- Grade a very inverse pairThe operating times of two very inverse relays at 6 kA.
- Grade three relays in seriesThe margins between three relays at 5 kA.
- Find a relay's time at ten times pick-upThe operating time of one relay at 2 kA.
- Check an instantaneous settingWhether a 4 kA instantaneous element clears an 8 kA fault.
- Grade an extremely inverse feederAn extremely inverse relay under a standard inverse incomer.
Ngā whakauru
He tauira mahi me ngā whakauru taunoa.
- Au hapa
- 1,200 A
- Ngā whakawhiti
- 2 rārangi
Wā whakakore Downstream
0.27s
- Wā whakakore Upstream
- 0.96s
- Tawhiti Downstream ki Upstream
- 0.68s
He āwhina hoahoa tēnei hua. Manatokohia ki te paerewa o nāianei.
Ngā hīkoi tātaitanga
- Au hapa1,200A
- Relay kua whakaraupapahia2
- Wā trip Downstream (IEC-SI)Hua0.27s
IEC 60255-151:2009
- Wā trip Upstream (IEC-SI)0.96s
IEC 60255-151:2009
- Mōrahi whakaraupapa Downstream ki Upstream0.68s
Mō tēnei tātaitai
How this is calculated
The tool plots the trip curves of inverse-time overcurrent relays. It then checks the grading margin between relays at one fault current. Up to four relays are allowed, listed from downstream to upstream.
- Fault current. You enter the prospective fault current. The tool uses it for every relay.
- Multiple of pickup. For each relay, the tool divides the fault current by the pickup current. A relay does not trip at a multiple of 1 or less.
- Trip time. For an IEC curve, the tool uses the IEC 60255-151:2009 equation, with the time multiplier setting. For an IEEE curve, it uses the IEEE C37.112 equation, with the time dial. The curve constants come from the standard.
- Instantaneous element. If the fault current reaches the instantaneous setting, the relay trips at a fixed short time.
- Grading margin. The tool subtracts the trip time of each relay from that of the next one upstream.
| Step | Table or clause | What it decides |
|---|---|---|
| Curve shape | IEC 60255-151:2009 | The trip time of an IEC relay |
| Curve shape | IEEE C37.112 | The trip time of an IEEE relay |
| Margin | Your relay list | The gap between each pair of relays |
Worked example
- Two IEC standard inverse relays at 1200 A. The downstream relay has a pickup of 100 A and a multiplier of 0.1. The upstream relay has 200 A and 0.25. The downstream relay trips in 0.27 s. The upstream relay trips in 0.96 s. The margin is 0.68 s.
Limits
The tool uses the ideal curve equations. It does not model relay reset time, overshoot or current transformer saturation. It does not read curve data from a maker. An instantaneous setting of 0 means none.
The margin is for one fault current only. Check the margin at the highest and the lowest fault current at the relay. The tool does not choose settings for you.
See also: IDMT curve 100 A feeder grading, IDMT grading for a main switch and submain and IEC 60255-151 IDMT curve constants.
Pātai
He āwhina hoahoa te hua. Manatokohia ki te paerewa o nāianei.
He aha te mahi a te tātaitai IDMT?
Ka tuhi te taputapu i te kauwhata trip o tae atu ki te whā o ngā inverse time overcurrent relays. Ka whakaatu ia i te wā trip o ia relay i te iahiko hapa ka uru e koe. Ka whakaatu anō ia i te grading margin i waenga i ia takirua relay i te rārangi.
Ko ēhea ngā kauwhata e wātea ana?
Ka whakaatu te taputapu i ngā kauwhata standard inverse, very inverse, extremely inverse me te long time inverse o IEC 60255-151:2009. Ka whakaatu anō i ngā kauwhata moderately inverse, very inverse me extremely inverse o IEEE C37.112. He tauwehe pūmau motuhake tō ia kauwhata, nō reira he rerekē ngā wā trip mō ngā tautuhinga ōrite.
Ko ēhea ngā uruhanga e tino nui ana?
Ko te momo kauwhata, te pickup current me te time multiplier e whakatau ana i te āhua me te tūnga o te kauwhata. Ko te iahiko hapa e whakatau ana i te wāhi e pānuitia ai te wā trip. He kōwhiringa te tautuhinga instantaneous. Ko te raupapa relay i te rārangi e whakatau ana ko ēhea takirua e whakatauritea mō te grading.
He aha ngā raru noa?
Kāore tētahi relay e whakaroa i raro i tōna iahiko pickup, nā reira ka kī te taputapu kāore he pickup i reira. Ka whakakore te tautuhi wawe i te kaupapa ki runga ake i tōna paepae. Ka puta he whakatūpato ina heke te matahiko grading ki raro i 0.3 hēkona, koia te tāunga paerewa a te taputapu. Ko ngā tautuhinga relay kei te wāhitau o te whārangi.
Ngā tauira mahi
- Dairy shed IDMT relay setting and gradingThree IDMT relays at a 3000 A fault, two grading margins and one curve inversion between the shed main and the farm incomer, read off the AmpSize relay engine.
- IEC 60255-151: IDMT curve constantsWhat IEC 60255-151 governs, which curve sets the IDMT tool carries, and a worked grading pair on standard inverse that clears in 0.21 s and 0.74 s.
- IDMT curve grading for a 100 A feederTwo standard inverse relays at 2000 A give a feeder trip at 0.23 s, an incomer trip at 0.99 s and a grading margin of 0.76 s, read off one chart.
Kōrero o muri
Ngā Clause me ngā Table e pānuitia ana e tēnei taputapu
- IEC 60255-151:2009 / IEEE C37.112-2018Inverse-time overcurrent curves
- IEC 60255-151 Table 1 / IEEE C37.112 Table 1IDMT overcurrent curve constants
Ia Clause me Table, me te pēhea i manatokotia ai ia tētahi
Ngā tūtohi i arotakehia whakamutunga i te 26 Sept 2026.
Ngā taputapu hononga
- Tātaitai fault rating tauraCheck that a conductor can withstand the fault current.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- Tātaitai Arc FlashEstimate the energy of an arc flash and its PPE category.IEEE 1584-2018IEEE 1584-2002
- Utu ngaronga pūngao taura ā-mahiWhat a cable size up saves in energy, cost and CO2.AS/NZS 3008.1
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