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ELECTRICAL SAFETY FOR UNEARTHED POWER SUPPLIES
•A-ISOMETER®
•Insulation monitoring devices
•Insulations fault location devices
The IT system
No live conductor of the system has a conductive, low-resistance connection
to the equipotential bonding system (earth). |
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Design of IT System
The IT system is supplied by an independent supply source like
- Distribution transformer for industrial purposes
- Control transformer
- Generator, power set
- Battery
- UPS converter
- Solar panel
Advantages of an IT System
- Increased Economic Efficiency
- Increased Operational Efficiency
- Optimized maintenance
- Extensive Protection against Fire
- Enhancement of Accident
- Higher Permissible Earthing Resistance
Insulation Fault in an IT system
- In IT systems (standard-compliant term for unearthed systems) the first fault does not have any negative influence.
- The first fault does not cause unwanted system shutdowns.
- A double insulation fault at different conductors is the same as a short-circuit.
In this case, fuses are protective devices
 
INSULATION MONITORING DEVICE
An insulation monitoring device monitors the ungrounded system between an active phase conductor and earth. It is intended to give an alert(light and sound) or disconect the power supply when the impedance between the two conductors drops below a set value, usually 50 kΩ.
Working Principle
Insulation Monitors superimpose a measuring signal, generated by signal generator G. On the occurrence of an incipient insulation fault, the measuring circuit between system and earth closed via the fault RF causing a voltage drop across the measuring resistance Rm, which is processed and evaluated by electronic circuitry. If the voltage drop exceeds the set value proportional to insulation resistance, an alarm is given. The signal has a DC component which is used to charge the system capacitances, thereby ensuring that the signal goes through the incipient fault. The nature of the measuring signal is very important as it should not affect operation of devices such as switched mode power supplies, computers, variable frequency drives etc. Further, the harmonics and other disturbances created by these devices, presence of filters connected to the system should not affect the measurement of the insulation fault.
The insulation monitor provides in advance, information for effective preventive maintenance thereby ensuring the availability of power supplies. It also prevents shock hazards in small and medium size low voltage power supply and distribution system. |
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Factors inflencing Measuring Technique
- DC voltages in the system
- High system leakage capacitances
- Variable, low frequencies
Active Measuring Principle
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DC measuring voltage (with inverter stage) |
AMP measuring principle (BENDER Patent) |
Principle |
Superimposition of DC voltage |
Superimposition of an Adaptive Measuring Pulse |
Application |
Pure AC systems |
Universal for all IT systems (AC, AC/DC, DC) in particular for systems containing converter drives |
Features |
For small leakage capacitances
DC insulation faults can lead to false measuring results |
For systems with high system leakage capacitances
automatic adaptation to the prevailing system conditions |
Construction
Operation
- The insulation monitoring device is connected between the phase conductors and earth.
- Continuously monitors the insulation resistance between the IT system and earth (PE)
- The measuring voltage UG generated by G is superimposed onto the system via the coupling R,a low pass and the measuring resistance Rm.
- An insulation fault RF closes the measuring circuit.The measuring current Im is flowing.
- Im causes a voltage drop Um proportional to the insulation fault RF at the measuring resistance Rm.
- Optically signals a drop in insulation resistance below a minimum value
- Must comply with the requirements of the product standard for insulation monitoring devices IEC 61557-8.
Product Overiew
Device Selection Check List
- Nominal voltage?
- AC, DC or AC/DC nominal voltage?
- Main circuit, control circuit or special application?
- System leakage capacitance?
- Response values?
- Expansion to an insulation fault location system?
- Special ambient conditions?
Applications
Scope of appl. |
Application field |
Typical device |
Standards and regulations |
Typical
applications |
control circuits |
IR125, IR420,IR425 |
DIN EN 60204-1 (VDE 0113-1) :1998-11,
IEC 60204-1:1997 |
Railway |
Signal towers,
Level crossings,
track conductors,
point heaters |
IRDH265, IR125,
IR207,
IR470LY2-40 |
DIN EN 50122-1 (VDE 0115-3):1997-12,
EBA approvals |
Construction
sites |
Mobile generators |
IR423 |
DIN VDE 0100-704 (VDE 0100-704): 2001-05, DIN VDE 0100-551
(VDE 0100-551):1997-08, IEC 60364-5-51
Ed. 5.0:2005-04, BGI 608: 2004-08 (Annex 4) |
Mines |
All systems >
AC 50 V
or DC 120 V |
on request |
DIN VDE 0118-1 (VDE 0118-1): 2001-11,
-2: 2001-11, -3: 2001-11 |
Chemical |
500 V IT systems |
IRDH275 /
IRDH375 |
Namur |
Electric
road vehicles |
Charging Systems |
on request |
DIN EN 61851-1 (VDE 0122-1): 2001-11
(corrigenda 200212),
DIN EN 61851-21 (VDE 0122-2-1): 2002-10,
UL2231-1: 2002 04,UL2231-2: 2002-05 |
Potentially
explosive
atmospheres |
Industrial trucks,
cables and
conductors |
IR425 |
DIN EN 60079-14 (VDE 0165-1): 2004-07,
IEC 60079, Ed. 3.0: 2002-10 |
Furnaces |
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on request |
DIN EN 50156-1 (VDE 0116-1): 2005-03 |
Fire brigade |
Fire-fighting
vehicles |
IR470LY2-4061 |
DIN 14867:2005-09 |
Airports |
Aviation ground
lighting systems |
IRDH1065,
FTC470XDP
(PROFIBUS) |
DIN V ENV 50231 (VDE V 0161-231):
1998-04 |
Variable Speed
Drives |
Main circuits |
IRDH275,
IRDH375 |
DIN EN 50178 (VDE 0160):1998-04 |
Lifting + hoisting
devices |
Control circuits |
IR125, IR420,
R425 |
DIN EN 60204-32 (VDE 0113-32):1999-06, IEC
0204-32:1998, EN 60204-32:1998 |
Industrial robots |
Control circuits |
IR425 |
DIN EN 60204-1 (VDE 0113-1):1998-11,
IEC 60204-1 Ed. 5.0: 2005-10,
EN 60204-1:1997 |
Scope of appl. |
Application field |
Typical device |
Standards and regulations |
Pwer plants/
Power distributions |
Battery systems |
IRDH275, IRDH375 |
DIN EN 50272-2 (VDE 0510-2):
2001-12 |
Medical
locations |
Rooms of Group 2 |
107TD47 |
DIN VDE 0100-710 (VDE 0100-710):
IEC 60947-6-1
IEC 60364-7-710: 2002-11 |
Military
facilities |
Mobile generators |
IR140RS |
DIN VDE 0100-551 (VDE 0100-551):
1997-08, IEC 60364-5-51
Ed. 5.0: 2005-04, BGI 608: 2004-08 |
Construction
sites |
Mobile generators |
IR423,
IR470LY2-4061 |
BGI 867, DIN VDE 0100-551
(VDE 0100-551): 1997-08,
IEC 60364-5-51 Ed. 5.0: 2005-04 |
Pipeline
construction |
Mobile generators |
IR423,
IR470LY2-4061 |
GW 308, 8.00 - Annex 2
(Mobile standby generators for pipeline
construction sites);
BGI 867: 2005-05 Annex 3
(Selection and operation of standby generators
on construction sites) |
Ships |
Control systems |
IRDH275,
IRDH375 |
DIN EN 60204-1 (VDE 0113-1):1998-11,
IEC 60204-1:1997, IEC 60204-1 Ed. 5.0:
2005-10 |
Ships (Navy) |
Submarines,
frigates,
mines-weepers
and speedboats |
IRDH275,
IRDH375 |
ASTMF 1134-94 (Reapproved 2002),ASTMF
1669-96
(Reapproved 2002) |
Safety
lighting |
Communal
facilities |
on request |
DIN EN 50172 (VDE 0108-100): 2005-10 |
Solar systems |
Solar power plants |
IRDH275,IRDH375 |
DIN IEC 64/1123/CD (EVDE 0100-712):
2000-08 |
Open cast mining,
Quarries or similar |
Conveyor systems
and
transport systems |
on request |
DIN VDE 0168 (VDE 0168): 1992-01 |
Traffic engineering |
carriage,
sleeping car,
locomotives |
IR5002,
on request |
DIN VDE 0115-1 (VDE 0115-1):2002-06 |
Benefits
- Extensive personnel protection
- High system safety and property protection
- Preventive fire protection
- High protection of the environment
- Prevention of malfuntions
- Less time and man power for fault location
- Prevention of unnecessary repair work
- Plannable downtimes
Extended maintenance-free periods |
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