OPEN PEN DETECTION AND SHUT DOWN SYSTEM

SYSTEME D'ARRET ET DE DETECTION DE PEN OUVERT

English Abstract

This invention is a unique way of electronically measuring an open PEN situation in a multi-phase system without reference to mother earth. If the floating voltage becomes dangerous, the device disconnects the circuit, avoiding a potentially dangerous situation to develop.

French Abstract

La présente invention est une manière unique de mesurer électroniquement une situation de PEN ouverte dans un système à phases multiples sans référence à la terre mère. Si la tension flottante devient dangereuse, le dispositif déconnecte le circuit, évitant une situation potentiellement dangereuse de se développer.

Claims

6
CLAIMS
1. A customer site entry device for creating a Virtual Neutral from a
three-phase
power source and measuring a voltage difference between the Virtual Neutral
and a
Protective Earth and Neutral (PEN) conductor, wherein the PEN conductor is a
customer
site conductor based on a Protective Multiple Earthing system,
wherein an elevated voltage difference between the virtual neutral and the PEN
conductor indicates that the PEN conductor is broken, and wherein the measured
voltage
difference is without reference to real ground.
2. The device of claim 1, further comprising a switching system to
disconnect the
three-phase power source, including the Protective Earth and Neutral
conductor, in the
event of the voltage difference exceeding a safe limit.
3. The device of claim 2, wherein the safe limit is a predetermined limit.
4. The device of claim 2 or 3, wherein disconnecting the Protective Earth
and Neutral
conductor is performed by disconnecting separate Neutral and Earth conductors
split from
the Protective Earth and Neutral conductor.
5. The device of any one of claims 2 to 4, wherein the switching system is
a five-pole
shunt trip, wherein three of the poles are for three respective phases of the
three-phase
power source, one of the poles is for disconnecting Neutral, and one of the
poles is for
disconnecting Earth.
6. The device of any one of claims 2 to 5, further comprising an output to
trigger an
alarm signal when the voltage difference exceeds the safe limit, to provide
warning of an
open-circuit Protective Earth and Neutral conductor, wherein the alarm signal
activates a
beacon or is read by a Programmable Logic Controller (PLC) or computer system.
7. The device of any one of claims 1 to 6, wherein the Virtual Neutral is
created by
the device connecting to each of three live conductors of the three-phase
power source,
and tying the live conductors but not the PEN conductor together in a star
configuration.

7
8. The device of claim 7, wherein the Virtual Neutral is at a centre point
of the star
configuration.
9. The device of any one of claims 1 to 8, comprising a voltage sensing
relay for
measuring the voltage difference.
10. The device of any one of claims 1 to 9, wherein at the customer site
the Protective
Earth and Neutral conductor splits into separate earth and neutral conductors.
11. The device of any one of claims 1 to 10, wherein the measured voltage
difference
is dependent on the PEN conductor being broken on a supply side and on
existence of a
phase-to-phase voltage difference.
12. The device of any one of claims 1 to 11, wherein the device is an
isolating
transformer-free device.
13. The device of any one of claims 1 to 12, configured to isolate a
customer site
distribution panel from the three-phase power source when the PEN conductor is
broken.

Description

CA 03141957 2021-09-24
1
OPEN PEN DETECTION AND SHUT DOWN SYSTEM
TECHNICAL FIELD
This application relates to an open pen detection an shut down system.
BACKGROUND
Electrical safety is of paramount importance, and there are various components
that are
used to ensure electrical safety in any electrical installation. Examples of
safety
components that are used to ensure safety are circuit breakers, fuses and
residual current
devices.
Circuit Breakers (MCBs) and fuses react to overload currents and are designed
to protect
the wiring from faults caused by overloading a circuit. This could occur
through a short-
circuit or simply by powering too many devices on the circuit.
Residual Current Devices (RCDs) are life-saving devices designed to shut off
the supply
if a live wire connects to earth, which can prevent a fatal electric shock if
a live wire is
touched, can provide some protection against electrical fires and will usually
trigger if a
cable is severed. In the United States and Canada, RCDs are referred to as
Ground Fault
Interrupters (GFIs). An RCD and a GFI is the same device.
Note: In the United States and Canada, 'earth' is referred to as 'ground'.
In the United Kingdom, like many other countries, the local grid has three
alternating
current (AC) phases plus a neutral connection, which is earthed at the local
sub-station.
This neutral connection is known as a Protective Earth and Neutral (PEN)
conductor. At
the customer site, the Protective Earth (PE) and Neutral (N) cables are split
out from each
other. This earthing system is referred to as TN-C-S system. It is also
referred to as
Protective Multiple Earthing (PME) in the United Kingdom.
Date Recue/Date Received 2021-09-24

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This system works well so long as the PEN conductor is working. If the PEN
conductor is
broken on the supply side, there is no longer a reference voltage for the
three phases. If
the load between phases is unbalanced (which it invariably is because there
will be
different loads on each phase), the voltage difference between phases can
become
substantial, with potentially fatal consequences. This scenario is called an
'Open PEN'.
The most common symptoms of an open PEN would be undervoltage, causing 'brown
outs' on a circuit with equipment unable to cope with the low voltage; or
overvoltage, which
can damage electrical and electronic equipment, risks causing fires and
electrocution.
MCBs and RCDs cannot identify an open PEN scenario and so a different form of
protection is required. This is usually provided by additional electrical
earthing when
power if brought into a building.
The recently released 18th Edition of the IET Electrical Regulations (BS7671)
has put
measures in place to try and deal with this situation. The measures available
are to
measure the voltage level on the neutral in the premises to earth (mother
earth) via an
electrical electrode as a reference point, converting the electrical
installation to a TT
Network by disconnecting the existing PEN and creating a separate PEN
conductor, or
fitting an isolation transformer.
Depending on the application, these options are not always possible. A good
example of
this would be installing electric vehicle charging points on an upper level of
a multi-storey
car park. Reliably earthing the supply before it is fed into the charging
points may not be
.. possible, whilst isolating transformers are big, bulky and expensive and
there may not be
a suitable space to install them.
SUMMARY
The invention is a unique way of electronically measuring an open PEN
situation in a multi-
phase system without reference to mother earth. If the floating voltage
becomes
dangerous, the device disconnects the circuit, avoiding a potentially fatal
situation to
Date Recue/Date Received 2021-09-24

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develop. This system has been implemented electronically without the need for
transformers.
This invention is different to the system devised by Gabrielsson, Flat and
Berman (patent
number US2018224488 (Al) ¨ 2018-08-09) that uses transformers to measure RCD
and
ground connections.
Kawamura (patent US2019086464 (Al) ¨ 2019-03-21) has devised a system to
detect
ground faults for DC applications. This is typically used for battery systems
and is not
suitable for AC grid connections.
This invention shall enable a three-phase power supply to be protected from an
open PEN
fault without the need for additional earth electrodes or isolation
transformers.
This invention shall protect every circuit from any upstream open PEN faults.
This invention is as defined in the independent claims.
The invention is more compact, lighter and significantly cheaper than
isolation
transformers.
The invention is easier to install than either isolation transformers or earth
electrodes.
The invention may also allow remote monitoring and reporting of open PEN
faults.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by the way of example and reference to the
accompanying drawings, in which:
Figure 1 shows an example of a typical TN-C-S earthing system layout with a
conventional
earth electrode;
Figure 2 shows an example of a TN-C-S earthing system using the Open PEN
device.
Date Recue/Date Received 2021-09-24

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DETAILED DESCRIPTION
Figure 1 does not describe the invention itself but explains how a
conventional electrical
system may be configured in countries like the United Kingdom that implement
TN-C-S
power distribution. It is used to illustrate the difference between a
conventional system
and the Open Pen device.
In Figure 1, the dotted box on the left-hand side of the drawing (point 1)
shows the output
components of a distribution sub-station. The three phase power lines (3, 4
and 5) are
tied together in a star, or Wye configuration (point 6). The centre point of
the star is the
neutral conductor (point 7). This is tied to mother earth using an electrical
electrode (point
8). Because this neutral cable has been tied to earth, it is referred to as
the Protective
Earth/Neutral (PEN) conductor (9).
The dotted box on the right-hand side of the drawing (point 2) shows the power
cables as
they enter a customer site. The PEN conductor is split at this point ( 10) and
is tied to earth
using one or more electrical electrodes (11). A separate earth conductor is
created at this
point (12).
The entire power cable, incorporating the three live conductors (3, 4 and 5),
the neutral
(9) and the newly created earth conductor ( 12) are then fed into a
distribution panel (13)
for distributing through the customer site.
Figure 2 shows the same system using the Open PEN device at the customer site.
Here,
a connection is made into each of the three live conductors (21, 22 and 23)
and tied
together in a star (Wye) configuration (24) creating a virtual neutral (25).
The voltage
difference between the virtual neutral and the PEN connector is measured using
a
conventional voltage sensing relay (26). If the voltage difference is greater
than a
predetermined safety limit, the voltage sensing relay closes it contacts. This
energises a
three phase five pole shunt trip (27), opening the contacts and thereby
disconnecting the
power conductors from the customer site.
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In addition to the voltage sensing relay disconnecting the shunt trip, the
output from the
relay can also be used to trigger an alarm signal. This signal could be used
to activate a
beacon or read by a Programmable Logic Controller (PLC) or computer system in
order
to provide remote monitoring of an Open PEN condition.
Date Recue/Date Received 2021-09-24

Representative Drawing