【 Weak current College 】 on residential total entry settings of leakage protection

The residential design code (GB50096-1999) of the total per residential power circuit breakers, earth leakage protection should have. "It is further clarified in the notes to" ... With leakage protection function of the circuit breaker on the arc fault current has a high sensitivity of the action, be able to cut off power supply to prevent the occurrence of electrical fires. "Here expressly laid down in each residential building total into the line set leakage circuit breakers, the authors of this analysis and discussion of issues, with the aim of research in engineering design how to properly implement the specification, in the system constitutes the equipment selection should pay attention to what issues.

1 with leakage protection function of the circuit breaker of choice

With leakage protection of circuit-breakers from function has two meanings: first, it has the function of the circuit breaker, can cut off the belt load circuit; second, it has the function of leakage protection, namely its own sequence with a zero checking device. Provisions referring to these two functions is an electronic unit, with two electrical unit to implement also fine. Because the target is a: preventing electrical fires.

Detection of the protector is a residual power through zero sequence transformers on the protected circuit in phase and neutral current of instantaneous values of Phasor and determination, judgment on the ground that the residual current leakage current. Consequently, the protector of current I △ n should consider two basic conditions: you must escape the normal leakage current (IL): I △ n ＞ IL; must be less than the minimum causes the fire lit current (IRmin): n is "I △ IRmin.

1.1 protector of current should be greater than normal leakage current value. According to the national standard of the protector installed and running (GB13955-92) 5.3 provides: "in accordance with the normal electrical lines, select leakage current protector of the rated current. Select the protector of the rated current, shall give due consideration to the protected circuit and device may occur in normal leakage current value, if necessary, the actual measurement is achieved via the protection circuit and device leakage current values; selection of the protector is not current, ratings shall be not less than electric lines and equipment for normal leakage current maximum of 2 times ". "Electrical circuits and equipment leakage current values and the classification of the installation of the leakage current leakage current characteristics and meet the requirements are as follows:

① for a single electrical equipment, current shall be not less than properly measured leakage current of 4 times;

② distribution lines of action current protector should be not less than the normal run of real leakage current, while 2.5 times should meet with the maximum leakage current of an electric equipment functioning leakage current of 4 times;

③ used to protect the entire network, the current shall be not less than real leakage current of 2 times.

In addition, the protector of the rated current shall have a certain margin, to accommodate the long loop of insulation resistance reduction, increase of electric equipment, as well as the season changes caused by leakage current increases.

1.2 leakage current size and the belt equipment and lines. Distribution lines and electrical devices of leakage current estimates in table 1 and table 3.

Table 1 220/380V single phase and three phase line buried, along the wall laying pipe wire per km through the leakage current unit mA/km

Insulation material cross section (mm2)

4610162535507095120150185240
PVC 525256627070798999109112116127
Rubber 27323940454949555560606061
PE 17202526293333333338383839

Table 2 motor leakage current: mA

Operation mode of rated power (kW)
1.52.25.57.5111518.5223037455575
Running 0.150.180.290.380.500.570.650.720.871.001.091.221.48
Motor starting 0.580.791.572.052.392.633.033.484.585.766.607.9910.54

Table 3 fluorescent lights, appliances and computer leakage current

Device name of the type of leakage current (mA)
Fluorescent lamp
Installed in a metal component 0.1
Installation on wooden or concrete widget 0.02
Household appliances handheld Ⅰ-device "0.75
Fixed type Ⅰ-device "3.5
Ⅱ-device "0.25
Ⅰ-electric equipment "0.75 ~ 5
Computer mobile 1.0
Fixed 3.5
Combined 15.0

Here is a three bedroom as an example look at the residence of normal leakage current:

Line (250m) BV-2.5mm 52 × 0.25 = 13mA

Household fluorescent lights (belongs to a metal component) 0.1 × 2 = 0.2mA

Fluorescent lamp 10 (placed on a wooden component) 0.02 × 10 = 0.2mA

Computer (TV), 3 desk 3.5 × 3 = 10.5mA

Handheld Ⅰ level 3 0.75 × 3 = 2.25mA

Fixed Ⅰ (air conditioning), 3 desk 3.5 × 3 = 10.5mA

　　Total 26.65mA press 27mA meter

1.3 in residential total into the line set protector to protect against electrical fires. Metallic short circuit of short circuit current, popular fuses, circuit breakers and other overcurrent protection appliances can effectively cut off power supply to prevent the occurrence of fire; small arc of short circuit current, overcurrent protection appliances are often not be able to cut off power supply and electric energy in up to a certain extent will ignite nearby combustibles resulting in a fire. Ground fault causes fire more is not only the chance of earth fault occurs, but also often with continuous arc forms.

Can cause ground currents and constitute arc's fault: ① conductors and electrical equipment for insulation damage; ② appliances or motor terminal block around the carbonization of melting points; ③ motor overload or choke coils of aging and the turn to turn short-circuit; ④ electrical equipment or installation of the device part with condensed water wet or product; ⑤ in electrical devices Cumulus with conductive dust or sediments.

Such a failure may cause incomplete short-circuit or grounding and causing a fire. When heating power to 60W ~ 100W, such as releasing in smaller areas of combustible, it would immediately cause a fire. When leakage protector out current parameters in 30mA, 0.1s and below can be used to prevent electric shock, indirect contact also cannot prevent direct contact with electric shocks and naturally capable of defending earth fault caused by ARC burns. When the voltage is 220V, adopt out current 300mA earth leakage protection device used to prevent electrical fire, 500mA's can be used as a preventive measure or backup protection.

In total the building into line Office install Protector, the entire building electrical circuits for maximum security, to fire such multiple electrical fire provides effective means.

2 in residential total entry Office install Protector application problems in

2.1 correctly choose Protector rated leakage current value. In the residential installation of total incoming Office protector and is used to cut off the power, when the switch malfunction would create unnecessary wide power outage, this possibility exists. Apartment large scope extended power is residents and property management Department is not acceptable.

Residential building total into line leakage current analysis:

Press the top 8 per layer, take over a coefficient: 27 0.75 × 8 × 0.75 = 162mA

A total of 18 floors, three-phase and total 144 households over a coefficient, 0.36 (per phase): 27 × 48 × 0.36 = 467mA

Press 3 multi-layer 1 ladder, 6 floor, take the same coefficient: 0.45 43 × 18 × 0.45 = 219mA

Total 6 doors, 108, 36 families per phase, take the same coefficient: 27 0.39 × 36 × 0.39 = 379mA

It should be noted here is borrowed over a factor in the calculation of the load, in a way that is not exact. Leakage current is different than the rated operating current, it is an electricity devices allow leakage current maximum, normally should be far less than this value. In addition, when the electrical equipment is not working, electrical equipment and wiring of the leakage current is exists.

Thus, if in the above line of residential total into only one protector of 300mA, may in his belt equipment and lines of leakage current is a normal range when undue trip.

2.2 total leakage current protective device malfunction. Earth leakage protection device reliability by the equipment of the capacitor current. When their on capacitance current Ⅰ c = 2 π f C U 0 not greater than the rated power leakage current can cause malfunction, electronic equipment, often with large capacity filter capacitors, capacitor is one end of the line through equipment grounding of PE.

Earth leakage protection device reliability with equipment of high harmonics. Power grid in the high-order harmonics, residential building equipped with a frequency in the elevator, pump, inverter air conditioner and other equipment also produces the high-order harmonics, when higher harmonic components is too large, its ground capacitance will become smaller, the leakage current increases, when more than the rated protector is not current may malfunction.

Power supply circuit inductive lightning over-voltage and overvoltage, it may cause leakage current protective device malfunction.

2.3 fire distribution circuit is located on the ground-fault protection. In order to prevent electrical fire, shall take all the lines of residential buildings and equipment under protector within the scope of protection, and the failure to cut off while the Mayor for fire power, (such as high-rise buildings fire pump, spray pumps, elevators, emergency lighting, exhaust fan, etc.), cut the power in the event of leakage, affect the evacuation and fire, causing more accidents or economic loss. According to the specification only allows loading alarm type protector. Obviously, for high-rise housing, power supply is the statue of the power of fire, do not allow for earth leakage protection device. Similarly, as the power supply of the spare power supply or supposes protector can use the alarm-protector to solve this problem? answer the question again, very difficult, the reason for this is: alarm-leakage protection does not protect the occasional arc-fault, and often this failure is caused by the source of fire; and the alarm type must have an alarm watch sites, and this has caused for maintenance management.

2.4 maintenance and management issues. For example, Beijing area of residential buildings in low voltage power supply most belong to the user, the power to implement "a table, measured to the home", the family table before electrical lines and equipments from the power to manage, as in General into the line supply Department together with the failure of the automatic power off leakage current protective device, the candidates have power. Because of the leakage current protective device reliability are not sufficiently demonstrated in Beijing has yet to reach a consensus with power. From the perspective of the power supply managementThe total number of residential building into line once the protector, power off, imagine what measures at the Conference? first is closing, the building of this switch should be set to lock in a dedicated distribution box or room to complete the switch. If you often trip or do not switch on again, and check out the point of failure would result in a prolonged outage that has been building, if jurisdiction is too large, it will cause residents of strongly reflect.

3 conclusion

"Every residential total power circuit breakers, earth leakage protection function should have." This prevents electrical fire in the large-scale implementation of measures, should be carried out with the concerned departments, developing technology implementation details. Each residential building as both adopted this measure must be taken to resolve the following issues: management issues, and coordination of the distribution system, the leakage current parameters calculation and selection of electrical appliances.