The formation and solution of high zero ground voltage

Zero ground voltage is a prominent problem that troubles the use of information equipment, and directly affects the stable operation of the system and the service life of the equipment. Properly handling the issue of zero ground voltage is crucial for maintaining the safe and stable operation of the entire computer room.

Electricity is one of the most important energy sources in daily life. Moreover, users in various industries have put forward increasingly high requirements for the quality of power supply. In addition to traditional measurement standards such as power supply reliability, voltage quality, and frequency quality, they also have higher requirements for zero to ground voltage.   

The issue of zero ground voltage is not strictly regulated in the national standard for computer room design, but it is often encountered in practical work. How does it arise? What are the hazards? How much range should it be controlled within?

1、 The formation of zero ground voltage. The rated output voltage of generator sets in power plants in our country is 3.15-20kV. To reduce line energy consumption, the output of general electrical energy needs to be boosted to 35-500kV through the step-up substation in the power plant, and then transmitted by high-voltage transmission lines to the substation in the receiving area, where it is reduced to 6-10kV. It is then sent to the user's distribution substation through high-voltage distribution lines and reduced to 380V low-voltage to provide users with electricity. For any user, the power supply line that provides them with power facilities is generally very long. Due to the unequal current between the transmission lines, there must be a zero ground voltage between the user end and the ground. However, if the zero ground voltage can be controlled within a certain range, it will not cause harm to the system or equipment. However, in certain situations, abnormal situations often lead to excessive zero to ground voltage, such as: (1) unbalanced load during three-phase power distribution; (2) The grounding resistance does not meet the specification requirements; (3) Insufficient or open circuit in the diameter of N (zero) and PE (ground) lines; (4) High frequency harmonics cause an increase in potential; (5) Electromagnetic field interference; (6) Using electronic power supply equipment such as UPS and electronic voltage regulators; (7) The patch panel used does not meet electrical standards; Previously, the main reasons for high zero to ground voltage were the first three factors. In recent years, with the widespread use of gas discharge light sources such as energy-saving lamps, as well as the widespread application of frequency conversion technology and large capacity thyristor rectifier devices, the zero to ground voltage value has become higher. Among the factors that generate zero to ground voltage mentioned above, items (6) and (7) are issues with user equipment. Taking the use of UPS as an example, UPS is composed of rectifier circuits, switching power supplies, etc. Due to the characteristics of electronic circuits and the presence of inductance and capacitance, the application of UPS in the system will cause a voltage difference between the output zero line and the input zero line, resulting in a voltage difference between the output zero line and the ground line.

2、 The hazards of zero ground voltage. The impact of zero ground voltage on the load is mainly manifested in three aspects: causing hardware failures and burning equipment; Misoperation that triggers control signals; Affects communication quality.

Excessive zero ground voltage can cause hardware damage. In general, the zero to ground voltage value cannot exceed 2V. The harm of high zero ground voltage, in addition to causing direct damage to electronic equipment hardware, may also lead to misoperation of control signals, causing equipment to start and shut down incorrectly. It may also cause an increase in error rate, packet loss rate, slow communication, and a decrease in transmission rate. Affects communication quality, delays or prevents normal communication. For computer equipment, high zero ground voltage can cause server speed to decrease, network switching speed to decrease, servers to shut down without reason, and even hardware damage. Sometimes, the server cannot start when the zero ground voltage is higher than a certain value (such as 2V). Therefore, for certain loads installed by users (such as HP mini computers, IBM servers, etc.), the manufacturer's hardware installation engineer will measure the zero ground voltage of the installation environment on site. Generally, it is required to be less than 2V, and if it exceeds this value, it will not be powered on. To avoid hardware failures, server managers must pay attention to the server's operating environment being completely normal. More important servers must not only operate in a constant temperature and humidity environment, but also have a power supply environment that meets standards. Not only should UPS be used, but a good grounding system must also be equipped to ensure that the zero ground voltage is below 2 volts.

3、 Control of zero ground voltage. Because zero ground voltage is an important factor affecting the reliability of machine operation, high zero ground voltage can cause machine failure or damage, so it must be controlled. Because the causes of the formation of zero to ground voltage are complex, control needs to be targeted. The main issues to consider and solutions are as follows: 1. Ensure load balancing. If the three power consumption items are unbalanced, the current on the neutral line N will increase, and the voltage difference between the two ends of the neutral line N will directly cause the zero ground voltage. Therefore, under possible conditions, it is necessary to balance the three-phase load as much as possible and make necessary adjustments regularly according to the changes in load usage. 2. By increasing the cross-sectional area of the neutral line, the line voltage loss of the neutral line can be reduced, thereby reducing the zero to ground voltage to a certain extent. 3. Establish a good grounding system and minimize grounding resistance as much as possible. When the grounding resistance is high, a very small current will generate a zero ground voltage, so it must be reduced. When calculating the diameter of the ground wire, after considering the maximum possible power consumption of the system and the basic safety requirements, it is necessary to specially calculate the cable length. Clear regulations need to be given for the ground wires with different diameters used on different floors at different heights. 4. Try to choose green electrical equipment that meets national regulations for harmonic interference. If necessary, corresponding equipment for suppressing high-order harmonics can also be installed to fundamentally purify the power grid. 5. At the same time, it is necessary to strengthen scheduled, regular, and targeted equipment maintenance to ensure the normal operation of the equipment and reduce high-order harmonics. 6. Choose a UPS with zero to ground voltage control capability or a smaller zero to ground voltage value. In the computer room, a large number of loads are servers, switches, and other types of loads. These loads themselves generate a large number of harmonics due to circuit reasons, which can cause cable heating and even result in the zero ground voltage of the input power supply exceeding the server's requirement of less than 2V. When selecting UPS, it is necessary to consider the control of zero ground voltage. Some types of UPS are specially designed to even output a zero to ground voltage of less than 1 volt. Strict supervision is required for the electrical construction involved in the secondary decoration of power supply and distribution. Due to the varying quantities of secondary renovation work, poor management can also affect construction quality and power supply system safety. 7. Installing isolation transformers is also an effective measure to reduce the zero to ground voltage. In cases where the zero ground voltage is too high and cannot be controlled by general methods, to ensure that the load can start up and operate normally, an isolation transformer can be installed to isolate the electrical connection between the input and output. However, this method is only applicable to UPS without built-in isolation transformers, usually by adding an output isolation transformer at its output end.