Surge protection

Industrial applications include various types of equipment that need to be protected from the effects of surges. They are costly to the company owner: the price may be enormous and the failure, or even replacement, of those devices would incur major financial loss, possibly putting the very existence of the company at stake. The key aspects, from the perspective of trade unions, are the employees: they operate electrical equipment and, in the event of a surge, their lives might be at risk. The facts mentioned above, as well as other causes, represent substantial reasons why one should seek protection from surges. This function uses internal and external protection from lightning, such as the air terminals, grounding, protective busbar, surge suppressors, all jointly referred to as surge protection devices, SPD. There are a number of companies that produce a plethora of devices, yet not all of them are suitable for industrial applications.

The heart of it all, as the case typically is, lies in a directive or a legal requirement. In this specific situation, it is Czech Technical Standard SN EN 62305 Lightning Protection, Parts I through 4. The text also defines individual types of loss, risk, lightning protection systems as well as level of lightning protection. There are four levels of lightning protection (I through IV) which specify the parameters of lightning; the protection levels are the function of the risk level. In most industrial applications, the building is classified Level I or II. This corresponds to the peak values of lightning current I_imp (current impulse with parameters 10/350 µs) being as high as 200 kA. A qualified estimate suggests that 50 % of the overall I_imp current is arrested by the air terminals and delivered into the grounding system. The remaining 50 % becomes equally distributed among the inputs (i.e. among the external contacts entering the building), typically to the IT and communication cables, metal piping and LV power supply cables.

With the growing awareness of the global warming and the limits to our fossil based fuels, the need to find better renewable source of energy is becoming apparent. The use of wind energy is a rapidly growing industry. Such installation are generally located on open and elevated terrain and as such present attractive capture points for lightning discharges. If reliable supply is to be maintained it is important that sources of over-voltage damage are mitigated. HAKEL Ltd. provides an extensive range of surge protection devices suited to both direct and partial lightning currents.

Whether it is a residential photovoltaic system on the roof of the family house, industrial photovoltaic powerplant or photovoltaics on the roof of an office building, you need to protect this installation against overvoltage by surge protection system. Hakel company spol. s r.o. has a big experience in this area and offers solutions for all types and sizes of solar power systems.

Lightning and surge arrester / photovoltaic systems / varistor / TYPE 1 + 2

SPC PV 600, SPC PV 800, SPC PV 1000
SPC PV 600 DS, SPC PV 800 DS, SPC PV 1000 DS

SPC PV is a lightning and surge arrester type 1+2 according to EN 61643-11 and EN 50539. It is designed for protection of positive and negative busbars of photovoltaic systems against the surge effects. These arresters are recommended for use in the Lightning Protection Zones Concept at the boundaries of LPZ 0-2 (according to IEC 1312-1and EN 62305). Particular varistor sectors are equipped with internal disconnectors, which are activated when the varistors fail (overheat). Operational status indication of these disconnectors is partly mechanical (by exserted red signaling target in case of failure) and partly remote monitoring (by potential free change over contacts – only DS types).

Due to the action of the drive, the power quality of the electrical environment can be compromised. That is, the drives can create voltage surges and harmonics on the system.

There are various technologies available that aid in correcting these issues. This application note focuses on applying surge protective devices (SPDs) to a drive system to mitigate the damage that can occur due to voltage surges while considering the effects of the harmonics on the surge protective device.

Often the incoming voltage is 480 V, but other voltages may be used. The incoming power is usually stepped down to a lower voltage (typically 120 Vac) that provides power to the control circuit. The control circuit contains sensitive electronics. 

Drive Input

Protecting the drive input is an essential step in protecting the drive system. Providing protection at this location prevents surge damage due to events propagated on the electrical system from upstream sources, external events such as lightning and switching surges created by the utility, and the interaction of multiple drives on the same system.

At this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry is not recommended for this location due to the fact that this location is typically more susceptible to impulse transients as opposed to ring wave transients.

Inverter Input

The inverter input is one of the most sensitive and critical areas of the drive itself. It is at this location that care must be taken and the proper survey conducted. You may install a parallel connected, frequency responsive circuitry device provided you have confirmation that within this drive that no additional capacitors have been installed to mitigate harmonic currents.

Control Circuit

The control circuit contains sensitive electronics that can be damaged by the environment created by the drive or by surges from external sources. Protection at this location is essential. Since this circuit is isolated by a step down transformer and it feeds sensitive electronics, a series connected SPD with frequency responsive circuitry is recommended for this location.

Drive Output

Protecting the immediate drive output is recommended when the length of the connection between the drive and the motor is longer than 50 ft (15 m) or if the connection is routed along an external wall or outdoors.

One reason for protecting at the immediate output when the length of the connection to the motor is long is due to reflected waves that can occur as the signal (often higher frequency) from the output of the drive reaches the motor and is then reflect back and forth between the drive and the motor. This action can create "voltage piling" – the reflected voltage adds to the nominal voltage and other reflected waves. The SPD will aid in reducing the voltage peaks of the reflected waves.

More importantly, if the connection between the drive and the motor extends outdoors, along a path that is exposed to the environment or close to the building’s steel structure, protection at this location is important to diminish the effects of direct lightning or induced voltage surges due to nearby lightning. These surges can cause damage to the drive, even if protection is provided at the motor input.

At this location, a parallel connected, voltage responsive circuitry device is appropriate (one without frequency responsive circuitry). Frequency responsive circuitry is not recommended for this location due to the high harmonic content of the signal due to the normal operation of the drive. Installation of frequency responsive circuitry devices at this location will lead to failure of the SPD. Utilizing a voltage responsive circuitry device at this location will eliminate this possibility.

 

Monitoring the status of ungrounded IT networks is a precondition for ensuring network safety and continuous operation, as required, in particular, in the health sector and in the heavy industries. The insulation monitoring devices monitor the insulation condition of the IT network and inform the operators immediately by acoustic or optical alarms about any insulation resistance decrease below the preselected R_crit level (against the PE protective conductor).

The insulation monitoring devices (IMD) offered by Hakel are used for easy application in ungrounded IT power supply systems in metallurgy, civil engineering, shipbuilding, in hospitals, the transport environment, underground and surface mine

IT POWER SUPPLY NETWORK

IT power supply system is an insulated system that has all active parts isolated from the earth or one point of the network grounded via high impedance. Inactive parts of the electrical installation are grounded. Ungrounded system increases the operational reliability and human safety. Therefore it is used in the metallurgy, mechanical engineering, shipbuilding, traction systems, public transport and hospitals. The advantage of the ungrounded system is that the device connected to this system can work continuously even in the case of first fault (so-called earth fault). The phase voltage of the undamaged phase (or phases in the three-phase system) is increased to the value of the delta voltage during the first fault. The system is safe if inactive parts are properly grounded. The reason is that there occur no bigger than safe current levels. The relevant responsible person must be informed about this failure and the first fault must be eliminated as soon as possible. However, the second fault (double earth fault) must result in immediate disconnection of the power supply system. The insulation monitoring devices or residual current relays are used for monitoring of the ungrounded system. These devices indicate the insulation level decrease below the set value.

With a gradual introduction of electronic protection systems sensitive to the overvoltage into the railway traffic, it is necessary to address also their protection, especially against dangerous effects of lightning strokes that may cause extensive damages to this equipment. A railway electronic signalling and interlocking system is a complex system that must be highly reliable and responsive in accordance with the needs of safe railway traffic. Individual functional units are located both inside and outside buildings, at the railway stations and on the lines, i.e. in the open environment where the induction from the lightning (impulse) currents has a great effect, both from the short and long-distance discharges. Seeking the optimum overvoltage protection thus requires a very special approach that is influenced mainly by the two basic aspects:
• The overvoltage protection installation must not influence a functional reliability and operational safety of the electrical signalling
circuits.
• Acquisition and operating costs should not be excessive.
On electrified tracks the overhead lines act as a protective lightning network and the lightning strokes are mostly caught by exposed parts of the overhead lines. By this the outdoor parts of the interlocking boxes are protected to a great extent. It must be, however, taken into account that the effects of the lightning impulses may be transferred via a decentralized electronic interlocking power supply system from the overhead line not only to the UNZ power supply source but also to the interlocking electric circuits.

International standard bodies and industry trade groups have written specifications that deal with the mitigation of effects of primary lightning strikes. More than 100 lightning protection codes and standards are in use by various countries and agencies around the world. Although none of these specifications deal directly with offshore oil lightning strikes, some that have been used in the offshore oil applications are shown below: IEC 62305 and EN 62305 standards. The Technical Committee TC81, (Lightning Protection) of the International Electrotechnical Commission (IEC) has released a series of five documents under the general heading “Protection against Lightning.” The five parts (Part 1, Protections of Structures against Lightning: General Principles; Part 2, Risk Management; Part 3, Physical Damage and Life Hazard; Part 4, Electrical and Electronic
Systems within Structures; and Part 5, Services) provide a comprehensive standard. ANSI/NFPA – 780-2008. Among the best-known sources of information for the protection of external lightning protection systems, the U.S. National Electric Code covers grounding, bonding, and shielding issues related to conducting primary strike currents to ground. API RP 14C – Seventh 2001 Edition, American Petroleum Institute – Recommended
Practice for Analysis, Design, Installation, and Testing of Basic Surface Safety Systems for Offshore Production Platforms. All of these specifications and procedures focus on mitigating primary lightning strikes and address the problems of grounding, bonding and shielding of primary conduction paths. Beside figure shows a typical example as applied to an offshore oil platform. Note the primary conduction paths and the focus of the primary current strike to the earth ground.This figure also illustrates the critical importance of maintaining low-impedance grounding and bonding of all metal cunstruction parts.

A lightning strike on an offshore oil platform causes many secondary transient effects. Inductive and capacitive coupling mechanisms expose secondary power and control lines to radiated and conducted electromagnetic interference (EMI). Inductively coupled conducted interference is possible energetically mitigate by rigorous applications of the surge protective devices (SPDs) and will be the main focus of this paper. Capacitively coupled secondary radiated interference is possible to liquidate by the use of shielding of power and control lines. The shield on all shielded lines must be connected to the primary ground conduction path. Inductively coupled conducted interference is a primary cause of failures for power and control circuits during a lightning strike. This conducted interference is present at all levels of circuitry on the platform. The sensitivity of the components being used plays a key role in the amount of protection required at the system and subsystem level. The energy required to damage typical components found in an offshore oil platform is shown in upward figure. As expected, the sensitivity, and therefore, the amount of required protection varies as a function of the power handling capability of the component.

The natural gas pipeline infrastructure, including transmission lines, distribution lines, processing plants, compressions stations, gate stations, and underground storage facilities, is susceptible to Iightning strikes. This infrastructure encompasses approximately 310,000 miles of natural gas transmission pipeline, 1.9 million miles of natural gas distribution pipelines approximately 3,000 compression stations, and the associated electronic supervisory control and data acquisition (SCADA) systems used to control the infrastructure. This vast size provides a high probability that there will be Iightening strikes on or near the natural gas infrastructure on a reccurring basis. In addition to the substantial size of the present world pipeline infrastructure, it is estimated that the combined global growth of the pipeline infrastructure under construction or in the planning cycle for 2012 will be 118,000 miles. The two major areas of growth are the Asia Pacific Region, (34,295 miles) and the North America Region (31, 951 miles).

HGS100 Ex

HGS100 Ex – Separating high power gas discharge tube HGS100 Ex for use in explosion hazards areas. It is intended for equipotential bonding of the installation parts of buildings or technological entities which are not interconnected operationaly. In case of p.d. (potential difference) origin between those parts, the high power gas discharge tube ignites and interconnects both parts for a transient time (typical value of internal resistance at startup of HGS100 Ex is 0,001÷ 0,002Ω). Recommended installation is inside of the buildings, outdoors, in the damp rooms as well as in the subterraneous areas. It is an explosion-proof gas discharge tube with flexible connecting cable for equipotential bonding acc. to IEC 61024-1 and also for the use in IT installations acc. to IEC 60364-5-54. It complies with EN 50014 and EN 50028 standards. It is recommended for insulated flanges and insulated screw joints bridging in cathodic protected parts of industrial technology.