Measuring and Auxiliary Circuits

Connect the PD 521 in accordance with the terminal connection diagram specified on the type identification label. The terminal connection diagram is included in the Supporting Documents supplied with the unit and is also given in Appendix E of this manual.

Copper leads having a 2.5 mm2 _{cross-section are}

generally suitable as connecting leads between the current transformers and the PD 521. Under certain conditions the connecting leads between the main current transformers and the PD 521 must be short and have a larger cross-section in order to handle the permissible burden on the main current transformers. Copper leads having a 1.5 mm2 cross-section are sufficient for the binary signal inputs, voltage inputs, the signaling and triggering circuits, and for the power supply input.

As a general principle, all connections run into the system must have a defined potential. Pre-wired connections that are not used must be grounded.

Connecting the Measuring Circuits of Distance Protection

The current and voltage transformers must be connected to the protection device in accordance with the standard schematic diagram shown in Figure 96. The default and factory setting of the protection device is based on this current transformer connection scheme (“line-side grounding“). Connection of the current transformers in opposition (“busbar-side grounding“) can be taken into account when making the settings (see Section 7). The PD 521 is always equipped with four current inputs.

96 Standard connection diagram for the PD 521

Connecting Protective Signaling

Depending on the operating mode selected, either a signal transmission device or pilot wires are required for signal transmission. Transposed lines should be used for the pilot wires. Two or four lines are required. If only two lines are available, there must be an all-or-nothing relay in each station for coupling received and transmitted signals. The coils of the all-or-nothing relays must be designed for half the loop voltage. Figure 97 shows the connection with two lines and Figure 98 the connection with four lines. The protective signaling transmitting relay can be set to Transm. relay break contact or Transm. relay make contact. In the first case the break contact must be wired and in the second case the make contact. The figures show the connection for the setting Transm. relay break contact (K1 and K2 are shown in the de-energized state). In addition, the PD 521 can also function together with the SV 35A protective signaling system or the V 34

comparator relay if care is taken to ensure that at least a pilot wire current of 10 mA is flowing.

Connecting Steady-State Ground Fault Direction Determination

If the PD 521 is to function using ground fault direction determination by steady-state values, then the current transformer T4 must be connected to a window-type current transformer or a current transformer in Holmgreen configuration. If the metal sheath of the cable is led through the window-type transformer, then the overhead ground wire must be led (insulated) through the core again before it is connected to ground. The cable sealing end must be attached so that it is insulated from ground. In this way any currents flowing through the sheath will not affect measurement.

For ground fault direction determination by steady-state values, the neutral-point displacement voltage - formed from the three phase-to-ground voltages - and the ground current are required as measured variables. Figure 99 shows the standard connection of ground fault direction determination by steady-state values. For this connection “forward/LS“ is displayed if a ground fault occurs on the line side. A different connection scheme for the current transformer can be allowed for by making the appropriate setting (see Chapter 7).

Connecting the Auxiliary Voltage

Before connecting the auxiliary voltage VA for the

PD 521 power supply, make sure that the nominal value of the auxiliary device voltage agrees with the nominal value of the auxiliary system voltage.

Polarity reversal protection is provided in the form of a rectifier bridge. To preserve uniformity with other protection devices (L+ on terminal with smaller number), L+ should therefore be connected to terminal 13. The PD 521 has an auxiliary voltage supply that can be

switched between ranges and is factory-set for the voltage range of VA,nom = 110 to 250 V DC or 100 to 230 V AC.

Before changing the auxiliary voltage range, turn off any connected auxiliary voltage. The components located behind the front panel are energized! The voltage range is switched by repositioning plug-in jumpers on the I / O (input / output) module. After

loosening four bolts on the front side of the front panel, the local control module (front panel and processor module) can be removed once the following plugs have been removed first:

¨ The tab connector on the case

¨ The tab connector on the lower circuit board (I/O module)

¨ The ribbon cable connecting the local control module (front panel and processor module) with the I/O module ¨ The ribbon cable connecting the local control module

with the optional ILSA interface (to fiber optics or to wire)

Where possible, disconnection of the ribbon cable between the processor module and the I/O module should be avoided. Should disconnection have occurred, however, then the device needs to be re-initialized by way of a cold restart.

In the upper portion of the I / O module, between output relay and current input transformers, are plug-in jumpers, which are plugged in as shown as follows, depending on the desired auxiliary voltage range.

100 Plug-in jumpers positioned for an auxiliary voltage of 110 to 250 V DC or 100 to 230 V AC (view from component side)

101 Plug-in jumpers positioned for an auxiliary voltage of 24 to 60 V DC (view from component side)

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