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发表于 2007-12-23 22:29:31
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Several methods to increase loadability
1. Enable the load encroachment function such as for SEL -321 Relay+ y' b$ B- @5 q* F
Enabling load encroachment features on existing programmable IED logic in SEL-321 relays will increase line loadability. The load encroachment feature of relay could be set 150 % and 0.85 per unit voltage at a 30 degree power factor angle. % f8 c0 N' H) d
2. Change the impedance relay characteristic from a circle to s lens for L-PRO 2200E, D60, and MICROMHO relays
$ }: ?5 \/ X& w s9 J8 m. bElectronic Relays was a mho distance type relay. That relay’s characteristic could be modified from a mho to lens. The characteristic angle IN L-PRO 2200E could be increased larger than 90 degrees while the Comp Limit in D60 and MICROMHO relays could be decreased less than 90 degrees.( W$ f! N% S& b2 }" x
3. Increase the angle of maximum torque (reach) for KD relays 8 q3 `( m p2 \8 K3 c
In KD case the factory MTA is 75 degree, a common angle for electromechanical relays. To increase line loading, MTA angle can be adjusted on some relays as far as 90 degrees. Such adjustments can increase line loadability as measured along the 30 degree load apparent impedance line.+ d: g: R. E! u$ F" ~# C6 P1 [: n
KD relay is a kind of electromechanical relays. It needs to increase the angle of Maximum Torque (MTA) to keep the Zload 30 point out of the 3Φ zone 2 impedance circle. This is accomplished with the removal of three compensation resistors which will change the MTA of the impedance circles to 90 degrees. 9 `. B, w; n2 f# b2 C# y
Modify KD settings as follow:
1 ?1 ~2 V3 X2 r" JFirstly, from Zload 30 point calculates the Required MTA.
& E: _$ h. z9 G! @% ?+ }7 yThe Required MTA = Arc COS (Zload30 Reach /Zone 2 Reach) +30
% W- P4 j( x4 u: p8 C+ b7 `' GA. If the Required MTA > 90 degrees, then need to shift MTA to 90 degrees and reduce the impedance reach at the same time.6 D! l+ \8 Z8 \! u
If the Required MTA < 90 degrees, then need to shift MTA to 90 degrees and not need to reduce the impedance reach. |
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