SNGR series neutral grounding resistorDetailed product description：

SNGR series neutral grounding resistor

（1） Introduction
The neutral point grounding resistor cabinet is mainly used for connecting the neutral point of the main transformer and the grounding grid in urban and rural distribution networks. The urban and rural distribution network mainly refers to the three voltage levels of 10kV, 35kV, and 66kV power grids, which are widely used and occupy an important position in the power system. With the deepening development of urban power grid renovation, the capacity of 10KV distribution network has rapidly increased, and the network structure is becoming increasingly perfect. In addition, according to the needs of urban construction, overhead bare conductors are gradually being replaced by cables and insulated wires. At the same time, fire accidents caused by overvoltage in switchgear and expensive household appliances are also common. Therefore, how to effectively and economically limit the overvoltage problem in the distribution network has become a key focus of current power supply and consumption work.
The neutral point of a 10KV distribution network can generally be divided into ungrounded system, resistance grounded system, and arc suppression coil grounded system. Due to the fact that choosing a grounding method is a comprehensive issue involving factors such as the insulation level of the line and equipment, communication interference, relay protection composition, and the safety and reliability of the power supply network, the power supply systems of China's distribution network and large industrial and mining enterprises have different practices. Previously, most of them used the operation mode of neutral point ungrounded or grounded through arc suppression coils. In recent years, some urban power grids have vigorously promoted the operation mode of resistance grounding.
In the mid-1980s, the 10kV distribution network in cities such as Guangzhou developed rapidly. A large number of cables were laid in the central area of the city, and the single-phase grounding capacitor current increased rapidly, reaching over 60A in 1987. Although arc suppression coils were installed, due to the large capacitance current and frequent changes in operation mode, it was difficult to adjust the arc suppression coils. In addition, some cables with low insulation levels were used. In order to reduce the overvoltage level and minimize the possibility of phase to phase faults, the neutral point was grounded through low resistance.
According to the research results of the Quzhuang substation in Guangzhou, using a neutral point grounded with low resistance, when Rn ≤ 10 Ω, in most cases, the single-phase grounded power frequency voltage can be raised and reduced to around 1.4 p.u. Considering the limitation of arc grounding overvoltage, during the process of arc ignition to extinction, the excess charge accumulated by the system can be leaked out through Rn within the second half of the power frequency cycle after extinction, and the amplitude of overvoltage can be significantly reduced. According to this requirement, the low resistance value of the neutral point should meet the following conditions:
Rn≤1/3ωC0
When Rn=10 Ω, the arc grounding overvoltage can be reduced to below 1.9p.u.
If the selection of neutral point resistance value is too low, the single-phase grounding current will be large, which will cause significant interference to communication lines; If the resistance value is too high, the relay protection action will be unreliable. Generally speaking, there is no problem with interference to communication lines when the current in the neutral point resistance is between 100-200A. Under these conditions, the neutral point resistance value of a 10kV overhead line is 28.80-57.74 Ω. For cable based distribution networks, according to Japan's experience, the interference problem with communication lines is not significant when the current in the neutral point resistance is between 400-800A. Therefore, the range of neutral point resistance values for 10kV cable distribution networks should be 7.2-14.4 Ω.
From the perspective of ensuring the reliability of relay protection actions, it should have high sensitivity when a single-phase grounding fault occurs. There are two types of grounding relays: one is the grounding overcurrent relay, and the other is the grounding direction relay that operates based on the direction of zero sequence current.
The sensitivity of protection is not a problem when using overcurrent relays in the event of metallic grounding. However, when grounded through a transition resistor, a significant portion of the overhead lines have single-phase grounding faults, resulting in high resistance at the fault point and some issues with the sensitivity of protection. For cable lines, the transition resistance during single-phase grounding is generally small, which has little impact on the sensitivity of relay protection.
Finally, starting from the requirement of limiting resonance overvoltage, when the cable line is particularly long, there may be a situation where j ω Le=1/j ω C, which can cause resonance. If the neutral point has appropriate resistance, the abnormal voltage on the healthy phase can be limited.
The method of grounding the neutral point through low resistance, especially when single-phase grounding is mainly used in distribution networks with overhead lines, will greatly increase the number of trips. If the ring network power supply cannot be achieved or the line is not equipped with reclosing, the number of power outages will increase, reducing the reliability of power supply. However, for cable based distribution, the fault rate is extremely low, and this problem is not prominent.
Based on the specific situation in China, it is recommended that distribution networks with cable based capacitor currents exceeding 150A can adopt low resistance grounding methods, with corresponding fault current levels of 400-1000A. For 10kV systems, the neutral grounding resistance value can be taken as RN=10-20 Ω.
（2） Typical schematic diagram of the primary system of a neutral point grounding resistor cabinet (for reference only)

（3） SNGR series neutral grounding resistance execution standard

DL/T 780-2001 "Neutral Grounding Resistors for Distribution Systems"
GB6450 "Dry type Power Transformers"
DL/T 620-1997 "Overvoltage Protection and Insulation Coordination for AC Electrical Installations"
GB 311.2-6 "High Voltage Test Techniques"
GB 1208-1997 Current Transformers
GB 4208-93 "Degrees of Protection Provided by Enclosures (IP Code)"
IEC289
IEEE 32-1972 Standard "Technical, Terminology, and Testing for Neutral Grounding Devices"
Other relevant national standards and power industry standards

（4） Types
Small resistance grounding resistor cabinet for distribution network
Resistance grounding resistance cabinet in distribution network
High resistance grounding resistance cabinet for distribution network
Generator neutral point resistor grounding resistor cabinet

（5） Variety product serialization
Applicable voltage: 3.3kV~35kV;
Allow flow: 5A to 5000A;
Nominal resistance: 0.1 Ω~1500 Ω;
Allowable flow time: 10s, 30s, 60s, 10min, continuous operation;
Entry and exit methods: upper and lower entry and exit, lower entry and exit, side entry and exit, side entry and exit;
Installation location: indoor, outdoor;
Allowable temperature rise: 760 ℃ for flow times of 10s, 30s, and 60s; When the flow time is 10 minutes, it is 610 ℃; 385 ℃ during continuous operation;
Current Transformer CT: Optional

（6） Ordering Notice
When placing an order, please provide the following information related to the product:
a、 Rated voltage of the system: Ue (kV)
b、 Nominal resistance value: (Ω)
c、 Rated short-time current: (A)
d、 Short duration power on time: (s)
e、 Grounding transformer capacity: (kVA)
f、 Shell form: indoor or outdoor type;
g、 Shell color: If the customer does not require it, computer gray will be used;
h、 Entry and exit methods: upward and downward, downward and downward, side entry measurement, side entry and downward, customers can choose;
i、 Is CT: CT ratio and capacity installed inside the cabinet;
J、 Customers with other special requirements can negotiate and resolve them when placing orders.

（7） Model meaning

（8） Basic technical parameters

Specification Model	Rated system voltage (kV)	rated voltage (kV)	Rated short-time current (A)	Short duration power on time (s)	20 ℃ nominal resistance value Ω (±5%)
SNGR3.3-100-10	three point three	one point nine one	one hundred	ten	nineteen
SNGR3.3-200-10	three point three	one point nine one	two hundred	ten	nine point five
SNGR6.3-200-10	six point three	three point six four	two hundred	ten	eighteen point two
SNGR6.3-400-10	six point three	three point six four	four hundred	ten	nine point one
SNGR6.3-600-10	six point three	three point six four	six hundred	ten	six point one
SNGR6.3-1000-10	six point three	three point six four	one thousand	ten	three point six
SNGR10-400-10	ten	five point seven seven	four hundred	ten	fourteen
SNGR10-600-10	ten	five point seven seven	six hundred	ten	nine point six
SNGR10-1000-10	ten	five point seven seven	one thousand	ten	five point eight
SNGR10.5-400-10	ten point five	six	four hundred	ten	fifteen
SNGR10.5-600-10	ten point five	six	six hundred	ten	ten
SNGR10.5-1000-10	ten point five	six	one thousand	ten	six
SNGR35-200-10	thirty-five	twenty	two hundred	ten	one hundred
SNGR35-600-10	thirty-five	twenty	six hundred	ten	thirty-four
SNGR35-1000-10	thirty-five	twenty	one thousand	ten	twenty
SNGR35-1300-10	thirty-five	twenty	one thousand and three hundred	ten	fifteen point five
SNGR35-2000-10	thirty-five	twenty	two thousand	ten	ten

SNGR series neutral grounding resistor