Friday, February 6, 2009

Frequently asked question on Siemens breakes

Q1) Must the neutral conductor always be connected to the left pole of the ACB?
ANS: On 4-pole circuit-breakers, the neutral conductor must always be connected all on the left.
Otherwise this can cause malfunction of electronic over current release.

Also for non-automatic breakers the neutral always has to be connected to the left phase (due to the design layout of the breaker).

Q2) Are the circuit breakers 3WL able to detect and evaluate:
• Power flow direction?
• Energy flow direction?
• Reverse current flow?
ANS: For the circuit breaker 3WL with electronic tripping unit ETU45B or ETU76B, equipped with the metering function (and voltage transformer) there are extended protective functions available as described in the operating instructions (revision 11.2006) on page 9-100.
These functions can be used for tripping the breaker..
These signals can be displayed on the ETU or made available as floating contact using a digital output module.
Using COM15, these data are accessible via Profibus-DP.

Please be aware that add-up values are resettled when the ETU is disconnected from the auxiliary supply.
Either, these functions - in addition to the delay time as given in the operating instructions - require a response time of about 1 second.

Q3) Is ground-fault detection with 3WL ACB in an IT-System feasible?
ANS: No, it is not possible to achieve ground-fault detection with 3WL ACB in an IT-System.
One has to use an insulation monitoring device for ungrounded networks.
These devices permanently monitor the insulation resistance between the ungrounded single or three-phase AC-supply and a protective conductor and instantaneously signal occurring faults.

We recommend the use of a 3UG insulation monitoring relay for ungrounded networks

Q4) Which maintenance and inspection work can be carried out on a circuit breaker?
ANS) Information about maintenance of the circuit breaker is included in the operating instructions, part 24; also it is given in separate link on this page. Furthermore maintenance and inspection have to be done according the requirements of the switchboard manufacturer or the end user.

Apart from an inspection of the contact system and the arc cutes the circuit breaker basically is maintenance-free.
Within the routine maintenance of the breaker some operations should be done (if there were no switching operations during service) to move the mechanical system.

Independent from this an inspection has to be done after any short-circuit tripping.

Q5) How is ground-fault protection achieved with 3WL circuit-breakers?
ANS: Vectorial summation current formation (method 1 - ETU27B or higher):
The three phase currents and the N-conductor current are measured directly.
The electronic trip unit determines the ground-fault current by means of Vectorial summation current formation for the three phase currents and the N-conductor current.
For 4-pole breakers all CTs are integrated, for 3-pole breakers an additional external CT for the neutral protection is required.
This Rogowski-coil 3WL9111-0AA2.-0AA0 or 3WL9111-0AA3.-0AA0, named -T5 in our documents, has to be wired to terminals X8.9 and 10 as shown in the operating instructions on page 9-124 (edition 11.2006).

Direct measurement of the ground-fault current (method 2 - ETU45B or higher):
A standard transformer with the following data is used for measurement of the ground-fault current:
1200 A/1 A, Class 1, 15 VA (5 A secondary cannot be used).
The transformer can be installed directly in the grounded neutral point of a transformer.
This CT (T6 in our documents) has to be wired to terminals X8.11 and 12; the polarity of the CT does not effect the detection.

Q6) What is the selection criteria for 3WL circuit breaker used for protection of capacitors?
ANS)According to IEC, capacitor units have to be appropriate for operation with a current, whose r.m.s value does not exceed 1.3 x the current flowing at sinusoidal rated voltage and rated frequency.
Furthermore, there is an excess of 15 % over the real value of the energy tolerated.
The maximal current for switching and permanent load for the circuit-breaker shall be 1.5 x nominal rated capacitor current.

Q7)For which applications of ACBs 3WL and MCCBs 3VL are the very low settings of the short time delayed short circuit protection Isd = 1.5 x Ir useful?
ANS)With the aid of the short time delayed short circuit protection Isd it is possible to inhibit trappings as consequences of rejection inrush currents or current spikes.
The specific setting value for Isd depends mainly on the existing application.
There exist generators with very low short circuit currents.
That’s why the short time delayed short circuit protection is provided with setting options down to Isd = 1.5 x Ir.
Furthermore the different Isd-setting options are useful for application specific discrimination considerations.

Q8) How can the ETU (electronic tripping unit) be activated to make the parameterization?
The correct state of the over current release is displayed by the green flashing "Active" LED in heart-beat rhythm.
The "Active" LED starts flashing at:

- current of 80A for frame size I and II,
- current of 150A for frame size III or
- supply of 24V DC auxiliary voltage (from ETU 45B)

When the current exceeds set operating current of over current release (I >= Ir), then yellow "Alarm" LED on the ETU turns on.

The "floating state" between activated and non-activated over current release, at load-currents close to activation-limit of circuit-breaker with ETU45B is displayed with the message "Waiting for Trip Unit".

Due to this, the protection function is ensured even without additional supply voltage. The power supply is provided by the internal current transformer.

Tripping characteristic shows the behavior of the over current release when it is activated via a current before the release. If release (instantaneous short-circuit release) happens immediately after switching on the breaker and due to this, the over current release has not activated yet, the opening time takes about 3 to 10ms longer.

Q9) May the 3WL circuit breaker be used in systems of e. g. 150 HZ or 400 HZ?


The electronic trip unit is designed for 50/60 HZ +-10 % - there were no tests for other frequencies.
At higher frequencies the energy transformers would overload the power supply unit of the ETU.

For 400 HZ the 3WN6 e. g. with trip unit type "B" (but not "N" or "P") can be used.
At this frequency the breaker has to be oversized per 30-40% due to higher eddy-current losses.
May be that for 800 A a breaker 1250 A has to be used, but the setting of the trip unit may remain at 800 A.

Q10) Can a 3WL be used with a voltage above 1000V?
Breakers 3WL12/3WL13 with option A05 (Ue = 1000 V) were tested with a voltage of 1000V +5% =>1050V.
They were not tested at any higher rated voltages Ue.
Therefore it is not allowed to use 3WL breakers for Ue > 1050 V maximum value.

Q11) Are there negative effects to be expected in the operation of 3WL with frequency converters?
Frequency converters generate harmonics and often cable-born noise voltages, mostly common-mode interferences, in the line supply.
Reasons are:
- Low-frequency harmonics caused by 6-pulse supplies.

- Switching reactors on the line side, causing high voltage peaks.
- Switching the IGBT of the converter with very fast switching times.
- Resonant circuits producing high voltage peaks.

Most important is to have EMC-correct design of system configurations:

- Metal cabinet parts must be connected together and must be grounded.
- Signal cables and power cables must be routed separately.
- Always use shielded signal cables.

Low-frequency harmonics are reduced using line reactors.
The electronic system of the ETU calculates the rms-value and is therefore suitable for systems being afflicted with harmonics. The ETU is tested according EN 60947-2, Annex F, including electromagnetic compatibility (EMC) tests, immunity tests and harmonics.

Attention should be paid to the use of frequency converters in IT-systems. In non-grounded line supplies these peaks cannot discharge to earth via PE/PEN conductor.

For ACBs switching frequency converters, especially in IT-systems, we suppose the use of an additional EMC-filter for the ETU. This filter is connected between CT and ETU and reduces noise voltages.

Ordering: Order code Z=F31 or separately by using order-no. 3WL9111-0AK32-0AA0.

Q13) How about the function of the thermal memory?
Thermal memory of 3WL operates in following way:
Shortly before tripping energy value data responding to the actual current flow are read into a clock unit and the time counter of the clock module is resetted.
The buffered clock unit automatically continues operating.
When re-energizing the energy value data as well as the time counter are read out from clock device and converted in values which are interpretable for protection functions.

Does the display of the ETU45B of the circuit breaker 3WL an auxiliary supply to show the measured currents or is the minimum current of 80 A resp. 120 A sufficient ?
If ETU45B is not supplied with auxiliary power while minimum current is present, then background light is deactivated.
The display, however, is active and shows the measured currents.
1 Test device

The handheld test device is used to verify the proper operation of the trip unit, the energy transformers and current transformers as well as the tripping solenoid F5 and the data display

1.1 View

(1) LED for operating voltage indication

(2) Control buttons

(3) 6 LED's to show test results

1.2 Preparations

- Switch off and isolate the circuit-breaker

- Note the setting values of the overload release

- Switch off the earth-fault protection at the over current release, if available (Ig = OFF)

- Setting value IR = 1.0 In

- Interrupt external voltage supply for the electronic system, if available

- Remove the cap from the test connector X25 of the trip

1.3 Connection
: If this sequence is not followed then there may be false tripping& false result

(1) Test socket at the over current release

(2) SUB-D, 40-pole (test device) to socket connector, 40-pole or, with ETU release 2 and higher, SUB-D, 40-pole (test device) to plug connector, 40-pole

(3) Voltage supply

(4) Test device

1.4 Voltage supply

The test device is supplied by an AC power system 230 V or 115 V, 50/60 Hz. The factory setting is 230 V.The changeover switch is located on the printed circuit board inside the test device.

1.5 Operation

The status test starts immediately after connecting the voltage supply and queries the various components and parameters of the trip unit. If the status test is successful, the "ETU STATUS" LED will light up. Otherwise, the "ETU STATUS" LED will flash. It is possible to draw conclusions about the fault cause from the way in which it flashes

The status test can be repeated any time by pressing the "START" button for at least three seconds

Note: The status test is not supported by the over current releases type
ETU25B / ETU27B / ETU15B with identification number less than 253030xxxxxx / 273030xxxxxx / 150704xxxxxx .By pressing the "L" button for app. 3 seconds while switching on the test device power supply, the status test can be skipped for these types

Testing the current transformers

To test the current sensors and energy transformers, press the "START" button briefly (less than 2 sec).

A lit-up LED confirms the proper operation of the corresponding transformer. If an LED flashes, the corresponding transformer is not available, not properly connected or defective. Energy-transformers within CT’s will be tested "OK", if within the limits of 3.5 - 12 ohms and with an inductance above 300 mH.
External earth-fault-CT within the limits of 2.5 - 11 ohms and inductance above 500 mH will be tested similarly.
The length of the testing-period necessary may reach 65 sec.

Result of neutral CT check (for ETU release 2)

A flashing light (1 second on, 1 second off) indicates an error in the area of the transducer of the neutral conductor. The cause of this will either be a missing transducer (e.g. no external neutral CT connected), a missing connection to the transducer or a faulty transducer.
A rapid flashing light (0.5 seconds on, 0.5 seconds off) indicates an error in the area of the energy transformer of the neutral conductor.
The cause of this will either be a missing energy transformer (e.g. if an external neutral CT is connected), a missing connection to the energy transformer or a faulty energy transformer.

Testing the tripping function

Note Over current releases type ETU25B resp. ETU27B with an identification number smaller than 250205 xxxxxx resp. 270206xxxxxx do only react to a test of the L-tripping function.

- Charge the storage spring by hand

- Close

To test the tripping function, press one of the buttons "L", "S", "I", "N" or "G".

The test of tripping function will fail, if the corresponding protective a function of the ETU is not activated or available.

The circuit breaker trips after the time delay plus 2 seconds. The tripping reason can be inquired through the "QUERY" button at the trip unit. The trip cause storage function is available only, if the trip unit had been activated for least 10 min before tripping. Otherwise, the trip unit doesn't have the corresponding protective function or is defective.

Testing the display of the measured values

Once a tripping test has been carried out, if the ETU is not activated, the storage capability of the tripping reasons must be checked using the Query button. To check the correctness of the measured values in the display or via remote transmission press the "I" and "N" keys simultaneously.

A current is successively simulated via the measuring transformers in L1, L2, L3, N and G for 30 sec. The LED of the respective transformer will flash. The test can be considered successful if current is indicated in the corresponding position.

Activation of trip unit

To activate the trip unit press the “N“and “G“keys simultaneously

The trip unit is activated up to pressing another key.
With this function the “T.U.-Error“-LED can be checked, if the status test had finished with the error “Trip unit defective“.

1.6 Finishing

- Restore the noticed settings
- Mount the Cover on X25

Check points during maintenance

Following points need to check while carrying out the maintenance activity of 3WL & 3WT air circuit breaker. This check points are applicable to the ACB of other make also. For better life of your breaker make the annual maintenance contract with us for detail contact

• Closing coil operation

• Shunt release operation

• U/V release operation

• Earth fault release operation

• O/L & S/C release operation

• Cradle mechanism checking

• Cradle plug contact

• Test/service limit switch operation

• Breaker operating mechanism

• Checking of main Fixed & moving contacts

• Auxiliary switch operation

• Switching lock mechanism

• Lamination block checking

• Arc chamber

• Spring charging motor

• Spring charging operation

• Gear box operation

• Insulation test (if required)

• Earth terminal

• Door interlock
Most of the customer doesn’t know which information has to be given while ordering the ACB spares parts & hence they face the difficulty. Firstly it is very important to identify the correct spare part & its exact name which is given in Function of different parts with image link on the page .Generally breaker MLFB is sufficient to order required spares.
But if breaker MLFB is not available then following information is required to order required spares.

Shunt coil: Supply voltage

Closing coil: Supply voltage

Under voltage coil: Supply voltage, whether it is with time delay or without time delay

Motorized operating mechanism: supply voltage

Safety shutter: Number of poles in breaker, Size of breaker i.e. SIZE I SIZE II or SIZE III

Current Transformer: Size of breaker i.e. SIZE I SIZE II or SIZE III

Electronic Trip Unit (ETU): Only type number of ETU

Draw out Mechanism: Number of poles in breaker, Size of breaker i.e. SIZE I SIZE II or SIZE III

Arc chute cover: Number of poles in breaker, Size of breaker i.e. SIZE I SIZE II or SIZE III

Pole Set (Main contact set= 1 Fixed + 1 Moving): Number of poles in breaker, Size of breaker i.e. SIZE I ,SIZE II or SIZE III, Normal Current carrying capacity, Breaking capacity of contacts in kilo Ampere like 65 KA,80 KA,100 KA.

Lamination Block: Size of breaker i.e. SIZE I, SIZE II or SIZE III, Normal Current carrying capacity, Breaking capacity of contacts in kilo Ampere like 65 KA,80 KA,100 KA.

Connecting Terminals on chassis: Size of breaker i.e. SIZE I, SIZE II or SIZE III, Normal Current carrying capacity, Its arrangement i.e. Horizontal, Vertical Etc.

Rating Plug: Current Rating

Recommended spares parts of breakers in stock

Following are the Spares of 3WL & 3WT breaker can be maintained in the stock to minimize the breakdown time.

1) Shunt coil

2) Under voltage coil (With or without delay)

3) Motorized operating mechanism

4) Current transformer

5) E.T.U. Release

6) Draw out mechanism

7) Wiring Harness

8) Arc chute

9) Main contact set (1Fixed+1moving)

10) Lamination blocks or Jaw contacts

11) Connecting terminals

12) Rating plug

Frequency of inspection of breaker

Contact assemblies need to be changed according their condition but at least after

10,000 operation for SIZE 1 & SIZE 2

5000 operation for SIZE 3

1000 operation for SIZE 2 & SIZE3 when used in1000V appliances

(Note: To calculate number of operation of circuit breaker you can use mechanical counter available as a option with circuit breaker)

Switchgear operator has to determine the inspection intervals depending on the breaker application condition but at least

• One time per annum

• After interruption of heavy loads

• After trips by over current release(Electronic trip unit)

Down stream connected non automatic circuit breaker have to be inspected also after 1000 switching operation, an inspection has to be comprise

• Arc chutes & contact system

• Mechanical functionality

• Main & auxiliary circuit, function & connecting quality

• Plausibility control of trip unit setting& correction, if necessary

Draw out guide frame with arc chute covers installed; have to be replaced after no more than three short circuit interruption of circuit breaker

Arc chutes& contact system must be replaced depending upon their condition, but latest after 10000 switching operation

Depending upon the circuit breaker stress it may also be necessary to replace the operating system after 10000switching operation