It is proposed that the turning point in the component current Ir0 is set to 1 times the rated current of the high voltage side to ensure that the turn to turn short circuit in the braking current is less than the rated current Ie Ir, there is no braking effect.
Differential current threshold criterion should not be too small, it is recommended to take Icd = (0.3 ~ 0.5) Ie.
The setting of the ratio braking coefficient can be carried out according to the following formula:
Kcd = Kk (Ktx / Fwc + Fph)
Among them, Kk is the reliable coefficient, take 1.3 ~ 1.5
Ktx for the same type coefficient, take 1
Fwc for the current transformer to allow the error, take 0.1
The Fph for the current caused by current transformer unbalanced relative error is 0.05.
Ratio braking coefficient Kcd recommended range of 0.3 to 0.7.Id =∣
![专业定制发电机保护测控装置加工](//l.b2b168.net/2019/01/26/09/201901260917566578534.jpg)
3.9 inverse time negative sequence overcurrent protectionPower system occur asymmetric short-circuit and three-phase load imbalance may be the negative sequence current flowing in the stator winding of the generator, and produce harmonic current in the rotor, rotor surface overheating caused, generator's inverse time negative sequence over the protection of rotor flow under the situation not long overheated rotor insulation degradation caused damage to the generator, discrimination protection of generator stator negative sequence current size, consists of three parts:
1) under the time limit: when the negative sequence current is greater than the lower bound value but does not meet the start value of the anti time limit, the alarm ** is delayed by the lower limit;
2) inverse time: when the negative sequence current is larger than the inverse time start value, according to the inverse time lag action equation I22-K t is equal to or larger than a action, type: I2-- generator negative sequence current standard? Value, K - generator operation value of negative sequence current in the standard, a generator rotor surface bear negative sequence current capability of constant;
3) the upper bound limit: when the negative sequence current is greater than the upper bound limit, the upper limit is delayed by the time delay.
![专业定制发电机保护测控装置加工](//l.b2b168.net/2019/01/26/09/201901260917544288964.jpg)
1)the maximum phase current of a side is less than 20% of the rated current, it is not sentenced to the side;
2)2) the maximum value of the phase current is greater than 120% of the rated current of the side;
3)3) served as the start of one side of the current than before the start of the increase.In the case of the above three conditions are not satisfied, such as one side at the same time meet the following conditions, then sentenced to CT break:
1)only one phase current is zero;
2) the remaining two phase currents are equal before starting the current.
3.3.2 differential current limit alarmIf the difference is greater than 15% of the rated current, after more than 10s discriminant, issued a warning **. Differential current limit, but not locked differential protection. The function and the monitoring function of the AC sampling circuit of the protection device
3.4 loss of magnetic protection
Generator loss of excitation protection for generator excitation current abnormal decrease or disappear completely lost magnetic fault protection, by the generator stator impedance as the main criterion, combined with low voltage and generator excitation system low voltage as auxiliary criterion, and have TV disconnection locking function, TV break send alarm **.
Its action logic is as follows:
![专业定制发电机保护测控装置加工](//l.b2b168.net/2019/01/26/09/201901260917533396534.jpg)
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