DE19502059A1 - Differential current protection system for single-phase transformer - Google Patents

Abstract

An auxiliary current transformer (Wh) is disposed between the star point of the partial winding of the transformer and earth for detecting a single-pole internal fault. A processing circuit processes the secondary current of the auxiliary current transformer as the current value corresp. to the null current. The protection system (SD) receives current proportional to the partial winding. Half of the secondary current (IStrn) of the auxiliary current transformer is used as the null current. An adaptive matrix is used to detect the current between the star point and earth.

Description

Single-phase power transformers can each have a single winding or two partial windings on the upper and lower voltage side. If two partial windings are present on one voltage side, then these can be connected in series in accordance with a Y winding in a multi-phase power transformer or in parallel in accordance with a D winding in a multi-phase power transformer. Fig. 1 shows a single-phase transformer T, each with two partial windings W _T01 and W _T02 connected in series on the high-voltage side and two partial windings W _Tu1 and W _Tu2 arranged in parallel on the _low- voltage side; The arrows drawn define the Stromrich device (positive) with respect to a current differential protection arrangement SD, which is connected via current transformers W₀₁ and W₀₂ and W _u1 and W _u2 .

It is known (H. Titze "mistakes and Error protection in electrical systems ", Vol. 2, pages 81 to 85), to adapt to different winding arrangements to provide a transformer intermediate converter. These but cause a considerable effort.

To reduce the effort for a current differential it offers a protective arrangement for a single-phase transformer itself that be with multi-phase power transformers known principle of switching group adaptation to apply here that, also with a single-phase transformer with matching solution matrices to work, as is the case with the previously known Current differential protection arrangement PQ 721 from AEG for Multi-phase power transformers is the case.

Since the phase shift between the windings in a single-phase transformer can only be 0 ° or 180 °, in a single-phase transformer with two partial windings, only the treatment of the zero currents is important for the implementation of the adaptation. If the two partial windings on one side of the single-phase transformer are not grounded (right side of FIG. 1), then the detected secondary currents can be used directly. The adapted currents I * and I * can then be described for this side of the transformer using the following matrix (1):

In the above relationship (1) means

I = detectable current in the conductor L1 on the high voltage side of the transformer T to be monitored
I = detectable current in conductor L2 on the upper voltage side of the transformer T to be monitored

A corresponding adaptation matrix would apply to the undervoltage side if - in deviation from the illustration in FIG. 1 - the partial windings on the undervoltage side were not grounded.

If, on the other hand, the partial windings W _Tu1 and W _{Tus are} grounded on the undervoltage side (left side of FIG. 1), then the zero currents are to be eliminated in a single-phase transformer in accordance with the known procedure for multiphase transformers. As a result, fault currents that flow through the current transformers as a result of earthing in the protected area even in the event of earth faults in the network are rendered harmless without any special external measures. The matrix equation for the adapted currents I * and I * is then:

The zero current elimination has the disadvantage that the difference tial protection in the event of earth shorts in the protection area (by the fac gate 1/2) is less sensitive

The invention is based on a current differential protection arrangement for a single-phase transformer with two overvoltage cables term partial windings and two low-voltage part windings, of which at least the partial windings one voltage side a common connection to earth have over regarding the single-phase transformer current transformers arranged on the upper and lower voltage side Flows through the secondary windings proportional to the secondary windings men is charged and in the in a calculation circuit the secondary currents taking into account a zero current corresponding current size phase-related Differential current is formed and its size is monitored, and sets itself the task of a current differential protection to specify order for a single-phase transformer, the even with partial windings of a single-phase trans connected to earth formators are characterized by a high sensitivity.

To solve this problem, the differential protection includes order according to the invention with its primary winding in the connection to earth-lying auxiliary current transformers, and the Arithmetic circuit processes the secondary current of the auxiliary current transformer than the current quantity corresponding to the zero current.

A major advantage of the current differences according to the invention tialschutzanordnung is that alone by one additional auxiliary current transformer and detection of the current between an adaptation matrix is used between the star point and earth can be, which leads to a differential current only results from an internal error. For outside mistakes Residual currents determined with the value zero.  

In the current differential protection arrangement according to the invention it has proven to be advantageous if the computing scarf half of the secondary current of the auxiliary current converter as the value corresponding to the zero current inspects.

To further explain the invention is in

Fig. 2 shows an embodiment of the current differential protection arrangement according to the invention, in

Fig. 3 shows the situation with a single-pole external fault and in

Fig. 4 shows the situation with a two-pole internal fault.

As can be seen in FIG. 2 in detail, in which parts corresponding to FIG. 1 are provided with the same reference numerals, the single-phase transformer T to be monitored is arranged in a power supply network with conductors L1 and L2, the windings W _To1 and W _{To2 of} the single-phase transformer T are connected in parallel or in a "triangle" on the high-voltage side. On the undervoltage side, the partial windings W _Tu1 and W _{Tu2 of} the single-phase transformer T are connected in series or in the "star". The star point S of the partial windings W _Tu1 and W _Tu2 is connected to earth.

In the course of the conductors L1 and L2, current transformers W _o1 and W _o2 with their primary windings W _Wo1p and W _Wo2p are arranged on the high-voltage side of the single-phase transformer to be monitored; Secondary windings W _Wo1s and W _Wo2s are connected via inputs E₁, E₂ and E₃ to a current differential protection arrangement SD, so that secondary _currents I and I are supplied via these inputs. Correspondingly, current transformers W _u1 and W _u2 are seen on the undervoltage side, via whose secondary windings W _Wu1s and W _Wu2s secondary currents I and I are taken from the current differential protection arrangement SD.

As can also be seen in FIG. 2, an auxiliary _current transformer W _h with its primary winding W _{hp is} arranged in the connection between the star point S of the windings W _Tu1 and W _{Tu2 of} the one- _phase transformer T. The secondary winding W _hs supplies a current to the current differential protection arrangement SD which is proportional to the current in the connection to earth. In an arithmetic circuit of the current differential protection arrangement SD, an adaptation matrix is calculated for the undervoltage side of the transformer T to be monitored, as is shown below:

If a single-pole external fault occurs, as is shown in FIG. 3, in a single-phase transformer T monitored by the current differential protection arrangement with supply from the high-voltage side, then it gives itself values for the currents according to the following equation system (4th ):

For the undervoltage side, the adjustment matrix is according to Equation (3) is used while the fitting matrix for the High voltage side by the following equation (6) represents:

The differential _currents I _Diff1 and I _Diff2 result from the following relationships (7) and (8):

If a pole internal fault occurs on the undervoltage side when supplying from the undervoltage side, as shown in FIG. 4, then the following conditions result with regard to the detected currents

With regard to the corrected or adjusted currents then

_Then follows for the differential _currents I _DIFFL1 and I _DIFFL2

This shows that in a current differential protection arrangement of the embodiment according to the invention, the sensitivity to a single-pole internal fault is very high. If, for the same fault case, a consideration is made without the current I _Strn , _i.e. without the use of an auxiliary current _transformer W _h , then the adjusted currents on the upper and lower voltage side result according to the following relationships (14) and (15):

The differential _currents I _Diff1 and I _Diff2 result from this

The sensitivity without taking into account the current I _Strn is therefore considerably lower for a single-pole internal error.

Claims (2)

1. current differential protection arrangement for a single-phase transformer (T) with two high-voltage-side partial windings and two low-voltage-side partial windings, of which at least the partial windings have a common connection to ground on one voltage side,

• - The current transformers (W _o1 and W _o2 ; W _u1 and W _u2 ) with currents through the partial windings (W _T01 , W _T02 ; W _Tu1 , W _Tu2 ) proportional to the single-phase transformer (T) on the upper and lower voltage side ( I and I ; I and I ) is acted upon and
• - in a calculating circuit from the secondary streams (I and I I, and I) including a corresponding zero current current variable (I _Strn) each phase based a differential current (I _DIFF1 and I _DIFF2) is formed and is monitored for its size,
  characterized in that
• - The current differential protection arrangement (SD) contains one with its primary winding (W _hp ) in connection with earth auxiliary current transformer (W _h ) and
• - The arithmetic _{circuit processes} the secondary _current ( I _Strn ) of the auxiliary current transformer (W _h ) as the current quantity corresponding to the zero current.

2. Current differential protection arrangement according to claim 1, characterized in that

• - The computing circuit takes into account half of the secondary _current ( I _Strn ) of the auxiliary _{current transformer} (W _h ) as the quantity corresponding to the zero current.