transformer differential protection relay

 
transformer differential protection relay is be appropriate for the transformer differential protection of the 35KV、10KV、6kV to the 400V.and the device not only have the function of the differential instantaneous trip protection but also the Perfect differential protection function of Proportional differential protection of two harmonic brake、CT line-break Locking ratio differential protection、CT line-break alarm.also the 485 communication、Ethernet communication、Optical fiber communication interface,is the best choice for two winding distribution transformer differential protection.
this device can be the most perfect high-capacity distribution transformer with the  9672 transformer protection measurement and control device (backup protection),the Economical and practical way is to choose the  972C Transformer integrated protection relay instead of the 9672 transformer protection measurement and control device and 9695 differential protection device If the main transformer differential protection is needed ,the  9692、9693(main transformer differential protection measurement and control device)can be your best choice.
 
Protection function
       differential current instantaneous trip protection 
       Proportional differential protection of two harmonic brake
       CT line-break Locking ratio differential protection
       CT line-break alarm.
 
Auxiliary function
Fault recording
 
Measurement and control function
   IA、IB、IC；Ia、Ib、Ic；DIa、DIB、DIC is electricity quantity
 
Communication mode
485communication；
    Ethernet communication;
 Optical fiber communication;
 
Principle of the differential protection
     The range of the differential protection：that is the range of the two sides or three sides that current mutual inductor contains,the  fault that is out of the range do not work.therefore the fixed value need not to cooperate with the border component,and then is the current instantaneous trip protection of non time limit to protect the inter-phase fault,circle fault and the grounding fault in the outline of the transformer windings.
 
Pilot differential current instantaneously trip protection   
    Which in essence reflect the protection act quickly the two side current of the transformer ,when the  interior transformer occurs serious fault or the external two side or three sides of the transformer or the CT occurs short circuit ,then act and trip quickly.
Protective action criterion：Icd >Isd 
 
among：
Icd  is the actual differential current of the same phase CT of the two side
 Isd is the differential instantaneous fixed current value
Any three of them meet the requirement  thatIcd >Isd  then the differential will work to trip all the switch of the main transformer.
   The differential current in the actual function=  Ih * cosφ1 + IL*ＫLｊｘ*cosφ2   
 
among：
    ＫLｊｘ（Unbalanced coefficient of low pressure side）= Ie2h（Two rated current of high voltage side）/ Ie2l（Low voltage side two rated current）
    cosφ1 is the actual angle of high pressure side；cosφ2is the The actual angle of the low pressure side.
    ＫMｊｘ（unbalance factor of the medium pressure side）= Ie2h（Two rated current of high voltage side）/ Ie2m（Two rated current of medium voltage side）
cosφ1 is the Actual angle of high pressure side；cosφ2 is the The actual angle of the medium pressure side.    
The imbalance coefficient of high pressure side was 1
Proportional differential protection of two harmonic brake（with the function of the CT line-break locking）
   The protection adopts the split phase type,that is any one of the Ａ、Ｂ、Ｃ Protection actions are outputed，The following criteria are all based on one phase.
   Rate differential element protection act when the following types are set up at the same time:
among：Ｉh、Ｉl respectively is the High, low voltage side current    Ｉsd is the Differential setting value of the instantaneous trip current;Ｉcdqd is the Differential protection door Kanding value;
Ｉzd is the  stalling current,the main transformer value of the second circle average value of both sides of the current；and the third value is maximum value of a fault entry;     transformer differential protection.pngis theTwo harmonic component of differential current    Ｉcd is the fundamental component of differential current;    Ｋ2 is the Two harmonic braking coefficient;
1)  Differential protection of ratio braking
998 Transformer differential protection device using the conventional ratio differential protection, the use of the principle of the two harmonic brake, reliably avoid the differential circuit in the differential current and the effect of the inrush current.Its motion equation is as follows:
    Icd＞Icdqd    Icd＞K1*Izd   （the or gate between them）
  among：Icd is the differential current，Izd is the brake current,K1is the Ratio braking coefficient ,Icdqd Differential current threshold value
   For double coil transformer：Icd＝| Ih＋IL |    Izd＝| Ih一IL |／2
Simple calculation in debugging:
  If the proportional differential act,then the  Icd＝| Ih＋IL | > Icdqd；
   Also meet with the demand of ：Icd＝| Ih＋IL | > K1*Izd = K1* | Ih一IL |／2
 On the formula is to take into account the vector calculation, if only the calculation of numerical value, assuming high, low voltage side phase just a difference of 180 degrees;
   The upper inequality is：Icd＝| Ih - IL | > Icdqd；
    Icd＝| Ih - IL | > K1*Izd = K1* | Ih + IL |／2
    Mode 1：if Ih > IL ；
Then ：Ih > IL +Ｉcdqd；Ih > IL*（2+ K1）/（2- K1）Ratio differential act 
Mode 2：ifIh < IL ；
   then：IL > Ih +Ｉcdqd；IL > Ih*（2+ K1）/（2- K1）
2)  Proportional differential protection of two harmonic brake
   In order to escape the magnetizing inrush current of the transformer in the closing moments, the device using second harmonic as magnetizing inrush blocking criterion, the movement equations for: transformer differential protection.png＜Ｋ2×Ｉcd   
among transformer differential protection.png is the two harmonics of A, B, C three phase differential current,IIcd is the corresponding three phase differential current，K2 is the two harmonic braking coefficient.As long as there is any phase to meet the above conditions, then the locking phase ratio differential protection.
Judgment method of the ＣＴ line-break 
 In order to prevent the CT relay and the protection false action,The device uses the function of setting up the time delay CT line-break alarm and the instantaneous CT line-break lock protection
  1)delayed CT line-break alarm：When any phase of the difference  of time is greater than 0.15Ie the another 10 seconds, the CT signal is sent out alarm,But not locked differential protection.This is also the AC sampling circuit self-test function of the 9695  transformer differential protection relay       
2)  Instantaneous CT line-break alarm:In the process of fault measurement，Meet any of the conditions then it does not carry out the CT line-break：The maximum phase current is less than 0.2Ie;   After starting the maximum phase current is greater than 1.2Ie.
3) A side current simultaneously meets the following conditions will be considered to be CT line-break：Only one phase current is zero; the other phase currents are equal to the starting current.