All the instrumentation and control systems used in the power station should be accurately connected to the ground. "Ground" is a common reference point site, which is defined by different names when applied in different situations. In the design of TSI cabinets, there are protective ground and signal ground to avoid noise interference. A correct grounding system can effectively suppress external interference, enhance the reliability of measuring instruments, and reduce factors such as interference generated by the system itself. It is an important guarantee for shielding technology. Poor grounding or inappropriate grounding points can cause significant electrical interference in the system, affecting its accuracy. Apart from the TSI cabinet, the TSI system of the steam turbine is a multi-point measurement system for large-scale equipment and structures. Therefore, it is even more necessary to avoid the formation of multi-point grounding to create a ground loop. During the system debugging process, each link needs to be inspected and tested before power-on debugging can be carried out.
Among the large-scale thermal power, combined cycle and nuclear power units supplied by Topteng Technology Trading Co.,Ltd, the commonly used monitoring instrument system brands are Bentley 3500 system, EPRO ATG6500 system and vibro-meter VM600 system. This article will briefly explain the grounding design and verification of the Vibrao-meter brand for users to refer to during debugging or troubleshooting. Please keep following this official account. We will further release relevant grounding requirements for other TSI brands in the future.

1.The signal input shielding terminal of the VM600MK1 system is grounded with the frame
If your company uses the MPC4/IOC4T MK1 series products of Vibrao-Meter, the resistance value between the Shield terminals of the six input signals of the IOC4T board and the frame housing is less than 1Ω. This work is tested before leaving the factory and can be retested during on-site debugging.
In addition, due to reasons such as raw materials, a production halt notice for this series of equipment has been officially issued. If your company has any spare parts requirements, please contact Topteng Technology Trading Co.,Ltd.

Note: This is only for display of our commonly used equipment. If you need to confirm more information about production suspension, please contact the supporting manufacturer or authorized dealer further.

2. The input signal of the MPC4/IOC4 MK2 monitoring and protection module is grounded separately
If your company uses the MPC4/IOC4MK2 series products of vibro-meter, then on the shielded terminal side of the cabinet input, the cabinet grounding copper bar is connected through the cabinet rail, and the resistance between them should be less than 1Ω. As shown by the red arrow in Figure 1.

Figure 1 Schematic diagram of the MPC4/IOC4 MK2 product being connected to the cabinet grounding copper bar through the cabinet rail

3. The VM600 frame housing is grounded
The grounding point of the VM600 system frame's casing is located at the grounding position at the power input terminal of the frame. As shown in Figure 2, at the position marked in red, where it is connected to the grounding copper bar of the TSI cabinet, the grounding resistance should be less than 1Ω. This work is tested before leaving the factory and then debugged and retested on site.

Figure 2 Grounding position of the frame shell

4. Grounding requirements during the installation and connection of sensors
1) Eddy current sensor
The eddy current sensor is mainly used for the measurement of signals such as relative vibration, shaft displacement, key phase, and differential expansion. The installation and electrical connection diagram is shown in Figure 3.

Figure 3 Schematic diagram of wiring and grounding of the eddy current sensor
Grounding requirements:
The housing of the eddy current sensor shares the ground with the machine housing through the installation bracket and does not require additional grounding.
The shielding layer of the connection cable from the COM terminal of the preamplifier IQS9xx to the VM600 frame should be connected to the shielding terminal of the signal input channel of the VM600 frame. A grounding bar should be set up at the entrance of the cabinet and grounding should be carried out here. The design institute needs to design a three-core shielded cable. During installation, it should be noted that the preamplifier needs to be installed in the terminal box through an insulating base plate.
A grounding bar is set at the incoming line of the TSI cabinet to ground the VM600 system frame.

2) Acceleration sensor
Large thermal power units use acceleration sensors to measure the absolute vibration of bearing housings, and their output signal is a two-wire current.
There are two usage methods for the acceleration sensor. One is that the output of the preamplifier is directly connected to the TSI frame via a cable for measuring the absolute vibration on the turbine side, as shown in Figure 4. Another type of preamplifier output is then connected to the TSI frame after passing through the isolation grid for the measurement of absolute vibration on the generator side, as shown in Figure 5.

Figure 4 Schematic diagram of wiring and grounding of the acceleration sensor without isolation grid

Figure 5 Schematic diagram of wiring and grounding of the acceleration sensor with isolation grid

Grounding requirements:

Probe side: The probe housing is grounded with the machine surface through installation bolts and no additional grounding is required.
Preamplifier side: The metal housing (conductive) of IPC707 is connected to its "COM" and "SHD" terminals. Therefore, IPC707 can be installed and operated with or without a direct electrical connection between IPC707 and GND.
Isolation grid side: The shielding layer of the transmission cable from the "sensor side" circuit should not be connected to the GSI127 electrical isolation device (" open shielding "). On the contrary, the transmission cable from the "monitor side" circuit must be connected to the forced grounding bracket at the entrance of the cabinet (containing GSI127). The GSI127 electrical isolation device does not require grounding and should not be grounded on its DIN rail either. The output of the isolation grid to the VM600 frame is wired inside the cabinet. If additional wiring is needed, please contact the sales department of Shanghai Turbine Works.
On the cabinet side: The shielding layer of the connection cable from the SH terminal of the preamplifier IPC707 to the VM600 frame should be connected to the shielding terminal of the signal input channel of the VM600 frame. A grounding bar should be set up at the cabinet entrance and grounding should be carried out here.

3) Speed sensor
Combined cycle units make greater use of speed sensors. As shown in Figure 6.

Figure 6 Wiring diagram of CV213


Grounding requirements:
Probe side: Built-in electrical isolation;
A grounding bar is set at the incoming line of the TSI cabinet to ground the VM600 system frame.


4) Absolute expansion sensor
The absolute expansion sensor is used to measure the thermal expansion value. Its output is a current signal. The connection and grounding of the sensor are shown in Figure 7.

Figure 7 Schematic diagram of wiring and grounding of the cylinder expansion probe


Grounding requirements:
Probe side: The sensor housing is grounded with the surface of the machine being measured through installation bolts, and no additional grounding is required.
The shielding layer of the connection cable from the sensor to the VM600 frame should be connected to the shielding terminal of the signal input channel. The design institute needs to design a three-core shielded cable.
A grounding bar is set at the incoming line of the TSI cabinet to ground the VM600 system frame.


5) CV211 watt vibration sensor +TSG202 transmitter
CV211 is a magneto-electric velocity sensor that was once used for the measurement of bearing vibration in some nuclear power steam turbines and some auxiliary machines. The bearing vibration measurement adopts the form of sensor + transmitter and is connected to the bearing vibration transmitter TSG202 through a direct cable. The wiring diagram is shown in Figure 8.

Grounding requirements:
Sensor side: The CV211 has a stainless steel housing material, which is connected to the equipment through stainless steel screws and shares the same ground with the equipment, eliminating the need for additional grounding. Transmitter side: The TSG202 vibration transmitter is powered by 24V and has a housing material of Polyamid (insulation). Field instruments powered by less than 36V do not require protective grounding unless there are special requirements.

Figure 8 Wiring diagram of CV211+TSG202 transmitter


6) WW00X eddy current sensor +TSW/TWW/TIW transmitter
The WW00X eddy current sensor +TSW/TWW/TIW transmitter was once used for monitoring the shaft vibration, shaft displacement and key phase of some nuclear power steam turbines. The sensor adopts a direct connection cable and is connected to the transmitter through a connection head. The schematic diagram is shown in Figure 9.
Grounding requirements: Sensor side: The WW00X housing is made of stainless steel and is connected to the equipment through stainless steel threads. It shares the same ground with the equipment and no additional grounding is required.
Transmitter side: The TSW/TWW/TIW vibration transmitter is powered by 24V, and the housing material is Polyamid (insulated). Field instruments powered by less than 36V do not require protective grounding unless there are special requirements.

Figure 9 Wiring diagram of WW00X +TSW/TWW/TIW transmitter

7) CE620 acceleration sensor +VM600 monitoring and protection system
The CE620 acceleration sensor is used for vibration monitoring of auxiliary bearings in some nuclear power units. It adopts the form of sensor + extension cable +VM600 monitoring and protection module. The schematic diagram is shown in Figure 10.
Grounding requirements:
Sensor side: The housing of the eddy current sensor shares the ground with the machine housing through the installation bracket and does not require additional grounding.
On the cabinet side: A grounding copper bar should be installed at the incoming line of the TSI cabinet for input grounding.

Figure 10 Schematic diagram of wiring and grounding of CE620

5. Grounding of the TSI cabinet
The TSI cabinet should be reliably connected to the on-site grounding copper bar. The grounding resistance between any metal part of the TSI cabinet and the VM600 frame shell and the grounding copper bar should be less than 1Ω.

The grounding copper bar of the cabinet is connected to the on-site grounding system, and the grounding resistance of the on-site grounding system shall not exceed 1Ω.