Is RCD a leakage protector?

Residual current operating protector

(RCD)

On

RCD

Residual current leakage protector

Abstract:

RCD

Theoretical basis of residual current leakage protector; fault current

"

Residue principle

"

; use

"

Last level protection principle

"

"

Operation Management

Management, Quality Tracking

"

Principles;

RCD

Technical misunderstandings of users.

Keywords: Kirchhoff's current law; Ampere's loop law; residual current transformer;

Technical misunderstandings of RCD

.

1. Overview

There are many discussions about

RCD

residual current leakage protector, and the key words are summarized as follows:

RCD

p>

RCD

Limitations in function;

The leakage protector refuses to trip;

The protector malfunctions;

Frequent movement of leakage protectors;

Technical misunderstandings of leakage protectors;

It is impossible to solve the problems of frequent movement and refusal to operate within the technical ideas of leakage protectors;

…

The description of the actual application effect of

RCD

residual current leakage protector is:

"

In the transformation of the two networks, a large number of residual current-operated leakage protectors were used. A few years later, it turns out that the phenomenon of damage to the leakage protectors and artificial release of operation is very serious. The problem of electricity consumption and safe electricity use is still serious. There are many reasons for this, but the direct reason is that the leakage protector frequently moves and refuses to operate, which seriously affects the normal use of electricity. Management and electricity users have lost confidence in leakage protectors and even given up on the renovation of the two networks. During the implementation of the project, leakage protection devices

--

residual current action protectors have been widely used. Practice has proved that the application of protectors

has greatly improved the performance of the project. It reduces

personal electric shock casualties.

It also plays a role in supervising the insulation level of the line.

The effect of safe electricity use is significant.

Experience at home and abroad has proven that,

In low-voltage power grids, installing protectors is an effective protective measure to prevent personal injury and death from electric shock, electrical fires and damage to electrical equipment.

”

“RCD

can cut off the ground fault of the protection circuit very sensitively, and can also be used as backup protection against direct contact electric shock. This has been used in our country for many years

RCD

has been proven in actual use. However, care should be taken in further use of

RCD

. To its shortcomings

"

......

In short, there are different opinions, each with its own praise and criticism. Different, sometimes contradictory, sometimes unified. Who is right and who is wrong? Right, where is right; wrong,

Where is wrong

…

2.

RCD

Theoretical basis of residual current leakage protector

Carefully observe

RCD

’s internal structure and installation location:

Line entry and exit One side is the power supply,

the other side is the load

(the side being protected)

The power phase lines and working zeros required for the load to work The wire must pass through a soft magnetic ring around which an induction coil is wound.

In complex circuits, we call the intersection of multiple branches nodes.

Kirchhoff's current law states that the algebraic sum of all branch currents about a node is always zero,

∑I

= 0

In other words, the algebraic sum of partial branch currents about a node is equal to the algebraic sum of the remaining branch currents. If the load equipment and line system protected by

RCD

are regarded as a

“

Node

"

, About this

"

Node

"

The algebraic sum of the currents of some branches (both the phase lines and the working neutral lines required for load operation) is exactly equal to the algebraic sum of the currents of the remaining branches (ground leakage branches). Simply put, it is to add the currents of all power phase lines and working neutral lines of load equipment and lines

and find their algebraic sum, which is exactly equal to the ground leakage fault current of the system at this time

∑I

Phase, zero

= I

Leakage

This is

RCD

Theoretical basis for detecting random ground leakage faults sensitively and instantly.

Ampere's circuit law states that the line integral of the magnetic field strength vector

H

along any closed path is equal to the current flowing through the surface enclosed by this path

The algebraic sum of )

RCD

The soft magnetic ring with the induction coil in the internal structure is an ampere closed loop.

Summing the currents, the magnetic flux in the soft magnetic ring is both

"

and the current

"

The magnetic flux generated is exactly equal to the magnetic flux generated by the ground leakage fault

of the load equipment and line system at this time.

The magnitude of the induced electric potential and the magnitude of the induced current in the soft magnetic ring induction coil are directly proportional to the ground leakage fault current.

So it is called a residual current transformer, not

"

Zero-sequence current transformer

"

When there is no ground leakage fault in the load system and there is no residual branch current, the algebraic sum of the phase line and working neutral line currents of the load system

is always zero, even if the phase line and the Short circuit, overload, phase loss, undervoltage, loss of voltage, overcurrent, etc. between phase lines, phase lines and neutral lines

All pass through

RCD

< The algebraic sum of the operating current and fault current between the branches of p> is always zero, and the magnetic flux in the RCD

soft magnetic ring is zero.

The induced potential in the induction line

is zero,

RCD

will not move, so

RCD

has no protection against short circuit, overload, voltage loss, phase loss, etc., so it is called

RCD

residual Current leakage protector. The circuit breakers currently produced are equipped with residual current transformers inside, which not only have short circuit, overload, voltage loss, overcurrent and other protection functions, but also have ground leakage protection function.

3. Fault current

"

Residual principle

"

RCD

The principle for the installation and use of residual current leakage protectors is fault current

"

The residual principle

"

It has been seen by us As nodes, load equipment and line systems that require leakage protection, all related power supply phase lines, working zero lines

N

and other work The branch current must pass through the magnetic ring of

RCD

;

Protect the neutral line

PE

, Test branch and other protection branch currents, test branch currents, and fault branch currents are regarded as remaining branches and are not allowed to pass

RCD

. For example, on the load side working neutral line of

RCD

N

Duplicate grounding wires and protective neutral lines are not allowed

PE

No entry

RCD

4.

“

Reasonable selection

p>

”

Principle

RCD

The residual current leakage protector can detect the ground fault current instantly, randomly and without dead zones, and its action is sensitive. The protection time is short when cutting off the power supply.

Therefore, as long as it is reasonably selected, installed and used correctly

RCD

the protector can protect personal safety, prevent electric shock accidents and prevent fires

Disasters will have obvious effects.

If the principle of scientific and reasonable selection is violated and the

RCD

protector is abused, the protector may malfunction or operate frequently, causing frequent power outages and large areas

p>

Power outages reduce the safety, stability and reliability of power supply, affecting normal production and life, which will of course cause people trouble.

The state promulgated the "Regulations on Safety Supervision of Leakage Protectors"

(Lao Anzi (

1999

)

No. 16

) and "Installation and Operation of Leakage Protectors

(

GB13955-92

) and other series standards and regulations. The following main principles should be followed when selecting a leakage protector:

1.

When purchasing a leakage protector, products from manufacturers with production qualifications should be purchased, and the product quality must pass the test.

2.

The power supply voltage and operation of the leakage protector should be determined according to the protection scope,

personal equipment safety and environmental requirements. Current,

leakage current and operating time

and other parameters.

3.

When the power supply uses leakage protectors for hierarchical protection, the selectivity of upper and lower switching actions should be met.

4.

Hand-held power tools (except

Class III

)

, mobile Household appliances for daily use (except

III

categories)

, other mobile electromechanical equipment, and

high risk of electric shock Large electrical equipment must be equipped with leakage protectors.

5.

Electrical equipment in construction sites and

temporary lines

should be installed with leakage protectors.

This is

"Technical Specifications for Temporary Electricity Safety at Construction Sites"

(

JGJ46-88

) as explicitly required.

6.

Socket circuits in offices, schools, enterprises and residential buildings, as well as socket circuits in guest rooms of hotels, restaurants and guest houses, must also be installed

Install leakage protector.

7.

Power supply lines and equipment installed in water, as well as moisture,

high temperature,

large metal occupancy coefficient and other Places with good conductivity, such as machinery, metallurgy, textile, electronics, food processing and other industries, as well as boiler rooms, pump rooms, canteens, bathrooms, hospitals, etc.

The place must be protected by a leakage protector.

8.

For fixed-line electrical equipment and normal production workplaces,

power distribution boxes with leakage protectors should be used.

Small electrical equipment for temporary use

should use leakage protection plugs (seats) or socket boxes with leakage protectors.

9.

When the leakage protector is used as a supplementary protection for direct contact protection (it cannot be used as the only direct contact protection)

, high sensitivity,

Fast-action leakage protector.

In general environments, the operating current should not exceed

30mA

, and the operating time should not exceed

0.1s.

, these two parameters ensure that if the human body is electrocuted

, the electrocuted person will not have pathological and physiological dangerous effects.

The rated operating current of the leakage protector in bathrooms, swimming pools and other places should not exceed

10mA

In situations where an electric shock may cause a secondary accident, it should be selected A leakage protector with a rated operating current of

6mA

.

10.

For electrical equipment that is not allowed to be powered off, such as passage lighting in public places, emergency lighting, power supplies for fire-fighting equipment, and anti-theft alarms

Alarm-type leakage protectors should be used to connect the alarm power supply to the audible and visual alarm signals to notify management personnel to deal with the fault in a timely manner.

Some people short-circuit or remove the leakage protector instead of carefully looking for the cause when the leakage protector operates. This is extremely dangerous and absolutely inappropriate.

allowed.

5.

"

Last level protection

"

Principle

It is necessary to use electricity safely, reduce electric shock accidents, and improve the reliability of power grid. This is a comprehensive requirement for leakage cut-off protection.

Increase the installation rate and operation rate of final-stage leakage protectors,

It is recommended to implement

"

Final-stage protection

”

Principle.

The main goal is to prevent direct contact and electric shock.

The respective protection areas are small and will not interfere with other users.

Second-level protection is system overall protection or branch protection. The protection scope is the main line (or branch line) of the low-voltage power grid

, the downstream line and the entry line.

It is recommended to consider that the rated leakage current of the upper level leakage protector is

2.5

～

3.0

times, the action time of the upper level leakage protector

is one step higher than the action time of the next level, which is about

0.1

～

About 0.2s

.

6.

“

Operation management and quality tracking

”

Principles

Leakage protectors are electrical products with compulsory safety certification implemented by the country.

Their quality will be directly related to the safety of users' lives and property

and must be strengthened and Carry out supervision over the quality of leakage protectors, implement dynamic management, improve the quality awareness of producers and operators, and prevent substandard and counterfeit products from entering the low-voltage power grid.

The operation and management of leakage protectors can be purchased and installed uniformly if conditions permit, and files can be established per household.

The person responsible for the operation should be clearly defined, and test trip operation records should be provided to correctly record the investment. Operation test conditions, regular trial tripping conditions, tripping conditions during operation, power recovery time, fault causes and abnormal conditions, etc.

7. Brief analysis

"Technical misunderstandings of RCD

"

Load equipment, line total There are distributed capacitances and inductances between the environment and the earth; electricity generated by high-order harmonics formed by nonlinear loads

Magnetic induction and electromagnetic radiation;

…

It will cause non-faulty normal leakage current in the power supply and power consumption systems. What's more terrible is that its size is uncertain

and changes with changes in environment, temperature, climate

...

etc. It is hidden in the residual current detected by the

RCD

protector and cannot be shaken off.

It always causes trouble. For example, after many families renovated their houses, the

RCD

action failed to close the circuit breaker, so they had to deactivate the

RCD

and forcibly send power. The reason is that the normal leakage current increases due to moisture in the room. Especially the

RCD of general protection and branch protection

protectors frequently vibrate, causing large-area power outages.

No fault can be found afterwards. The normal leakage current of the system changes at any time and increases instantaneously. The uncertain normal leakage current makes the practical application of RCD protectors encounter insurmountable difficulties. Experience tells us that

RCD

protector implements

"

last-level protection

"

p>

The correctness of the principle.

In the

TN---C

power supply system, the working neutral line

N

and Protecting the neutral line

PE

Shared a common neutral line and passed it

RCD

When the zero-load equipment leaks,

Phase occurrence

—

Zero short-circuit current causes the fuse to blow,

sensitive action

RCD

But there is no action,

Is it ridiculous? !

Actually, this is not

RCD

’s fault, but the installation user’s ignorance. The correct installation method should be to first repeatedly ground the neutral line at the three-phase four-wire household line; pull out a dedicated protective neutral line from the repeated grounding point

PE

, and the working neutral line

N

are independent of each other.

The household line is improved to supply power in a three-phase five-wire system.

TN---C---S

System; the single-phase household line is three wires, and the neutral line is protected

PE

No entry

RCD

. This way

the above joke won’t happen.

(The vast number of old residents in the city

RCD

are still in the above joke)

In addition, there is another situation Yes, also in the

TN---C

power supply system, the

RCD

rear load side is repeatedly grounded, causing

RCD

Frequent vibrations for no reason,

Unexplained power outages,

seriously affecting normal production and life.

The reason is that this connection method causes

RCD

The external system on the power supply side passes through

RCD

The repeated ground current of the ground electrode inside the load side becomes residual current. The solution is the same as above.

In the

TN---S

system, if the

RCD

rear load side , the working neutral line

N

Let the protective neutral line be grounded repeatedly.

In the

TN---S

system, if the

RCD

rear load side , use the working neutral line

N

as the protective neutral line

PE

, or use the protective neutral line

PE

Treat as working neutral line

N

Mixed use will cause

RCD

Frequent movement and failure to close. The reason is that this connection method turns the operating current into a residual current, causing the RCD to operate.