What we inspect in high voltage installations
High voltage equipment for transforming, distributing and consuming electricity is designated electrical equipment (Section 3(1)(a) of Government Decree No. 190/2022 Coll.), and its operator must have it inspected. We inspect the whole path of the electricity, from the HV connection to the low voltage switchboard in the transformer station.
- Brick-built, kiosk (compact) and pole-mounted transformer stations
- HV switchgear and switchboards: cubicles, circuit breakers, disconnectors, fuses, instrument transformers
- Oil-filled and dry-type HV/LV transformers
- HV cables: tests after laying, repair or jointing, inspection of terminations and joints
- Overhead HV lines and connections owned by the customer
- Earthing and equipotential bonding of the transformer station
- Protection devices and their settings, interlocking, signalling and emergency shutdown
- The associated LV switchboard in the transformer station
Who we carry out HV inspections for
Only equipment that is part of the transmission or distribution system of a licence holder, and connections operated by the distribution system operator (the distributor), is exempt from periodic inspections. Even for them the exemption applies only if safety is ensured by a preventive maintenance plan (Section 21(1) of Act No. 250/2021 Coll.). A transformer station owned and operated by a municipality or a company does not fall under this exemption.
- Municipalities and towns: their own transformer stations at wastewater treatment plants, waterworks, sports facilities and sites
- Manufacturing companies and industrial sites with their own transformer station or switchgear
- Developers and investors: initial inspection of a new transformer station and HV connection before it is put into operation
- Operators of photovoltaic power plants connected to the HV grid
- Managers of sites, hospitals, schools and shopping centres supplied from the HV grid
Initial, periodic, extraordinary and partial inspections
An inspection is also required after a change in the parameters of overload and short-circuit protection or of protection against electric shock (Section 6(4) of Government Decree No. 190/2022 Coll.), for example after reconfiguring the protection devices or replacing a circuit breaker or fuses on a feeder.
- Initial inspection – before new equipment is put into operation and after installation, repair or relocation that may change its properties (Section 6(2) of Government Decree No. 190/2022 Coll.); after reconstruction it is also required by Section 20(6) of Act No. 250/2021 Coll.
- Periodic inspection – repeated at intervals under Annex 4 of Government Decree No. 190/2022 Coll. and the inspection, maintenance and revision rules
- Extraordinary inspection – based on a special requirement of a regulation, standard, authority or owner, e.g. after an accident, fire, flooding or when previous inspection reports are missing; the inspection report then states its reason (Section 10(1)(e) of Government Decree No. 190/2022 Coll.)
- Partial inspection – an inspection of only part of the equipment, e.g. a new HV cable or a replaced transformer; when an initial inspection is done in parts, one summary inspection report is issued before handover to permanent operation (Section 10(2) of Government Decree No. 190/2022 Coll.)
How often is an HV inspection carried out?
Annex 4 of Government Decree No. 190/2022 Coll. has no separate line for transformer stations, switchgear, HV cables or overhead lines. Its intervals are set according to the building and the area in which the equipment is located, and they apply to all designated electrical equipment, including HV:
- Buildings for production, education, accommodation and medical purposes – 3 years
- Buildings which, under the fire safety solution, allow the presence of more than 200 people – 2 years
- Areas with a risk of fire and explosion, wet areas and areas with permanent presence of corrosive or polluting substances – 1 year
- Where the Annex sets no interval, the interval follows other regulations and standards; for transformer stations and switchgear it is determined by the environment in Table 1 of ČSN 33 1500 (e.g. basic and normal environment 5 years, outdoor and under a shelter 4 years, damp and dusty 3 years, wet 1 year)
- If the manufacturer specifies a shorter interval in the accompanying documentation, the manufacturer's interval applies (Section 7(2) of Government Decree No. 190/2022 Coll.)
Rules that are often forgotten
- If several intervals apply to the equipment, the shortest one applies (Annex 4 of Government Decree No. 190/2022 Coll., additional information (a)) – so a brick-built transformer station in a production site has an interval of 3 years, not 5
- A periodic inspection must take place in the year in which the interval since the last inspection ends (additional information (b))
- An operator with a preventive maintenance plan may set intervals of periodic inspections of up to twice the length in it (additional information (c)) – only if the checks and maintenance under it are actually carried out and recorded
- For equipment that must for serious reasons operate continuously, the periodic inspection may be carried out at the nearest interruption of operation, at the latest in the year following the end of the interval (ČSN 33 1500, clause 3.5)
How an HV inspection works
- Documents – we go through the documentation, the previous inspection report, maintenance records and the inspection, maintenance and revision rules; based on them we propose the scope of the inspection and prepare a non-binding quote
- Scheduling and shutdown – we agree the date with you and, where a de-energised state is needed, also with the distributor; we prepare and handle the shutdown request for you
- Visual inspection – the condition of switchboards, the transformer, cables and lines, covers and barriers, marking, diagrams and warning signs, accessibility and external influences (Annex 1 part A of Government Decree No. 190/2022 Coll.)
- Measurements and tests – earthing, continuity of protective conductors and bonding, insulation condition, HV cable tests, function of protection devices, interlocking and signalling and, on the LV side, also automatic disconnection of supply (Annex 1 part B)
- Evaluation – we compare the results with the documentation and standards and for each fault state the provision of the regulation or standard that is violated
- Inspection report – the conclusion on whether the equipment is safe to operate, measured values, faults and the recommended interval of the next inspection (Section 10 of Government Decree No. 190/2022 Coll.)
What to prepare before the inspection
The list is based on Annex 2 of Government Decree No. 190/2022 Coll. If a document is missing, the inspection does not stop because of it – in the inspection report we state what needs to be supplied.
- As-built project or drawing documentation and a single-line diagram
- The previous inspection report and records of checks, maintenance and rectified faults
- The protocol on determining external influences, if it is not part of the documentation
- The inspection, maintenance and revision rules, or the preventive maintenance plan
- Documents on the protection settings and the accompanying documentation of the transformer and switchboards
- For an initial inspection also the installation test records, routine test protocols of the products and details of the installation company including its authorisation number
- Access to the transformer station and switchgear, keys and the contact of the person responsible for the electrical equipment
- Consent to the shutdown and the supply point details for the request to the distributor
Who may carry out an HV inspection and what you receive
An inspection of designated electrical equipment may be carried out only by a company with the authorisation and an inspection technician with a certificate of professional competence (Section 20(2) of Act No. 250/2021 Coll.). HV inspections are carried out by an inspection technician with a TIČR certificate.
We follow Act No. 250/2021 Coll., Government Decree No. 190/2022 Coll., ČSN 33 1500 and the standards for equipment above 1 kV: ČSN EN 61936-1 (Electrical installations exceeding 1 kV AC) and ČSN EN 50522 (Earthing of power installations exceeding 1 kV AC). Safety at work during the shutdown is governed by ČSN EN 50110-1 (Operation of electrical installations).
- The inspection report in electronic form, signed with a recognised electronic signature (Section 10(1)(d) of Government Decree No. 190/2022 Coll.)
- Measured values and a list of the measuring instruments used
- An overview of faults with a reference to the violated provision and a clear description of what needs to be repaired
- The recommended interval of the next inspection and, on request, monitoring of its date
When the inspection does not pass
Faults endangering safe and reliable operation must be removed by the operator without undue delay after the inspection report is issued, other faults within deadlines the operator sets itself (Section 20(5) of Act No. 250/2021 Coll.). Equipment whose condition immediately endangers safety must be disconnected and secured against switching on (Section 7(8) of Government Decree No. 190/2022 Coll.). After the repair we verify that the faults have been removed and issue a new inspection report.
Operating equipment without an inspection carried out within the set interval and scope is, under Section 20(3) of Act No. 250/2021 Coll., a state endangering the safety of work and operation.
Free monitoring of inspection dates
We enter the date of your next HV inspection in our records and contact you before the end of the interval in good time, so that there is time to arrange the shutdown with the distributor. Just register on the "Inspection deadline monitoring" page – free and with no obligation. We set the price of the inspection individually according to the scope, and the quote is non-binding.
Our seat is in Pardubice. We also carry out HV inspections in Prague, Hradec Králové, Náchod, Rychnov nad Kněžnou and their surroundings.
Frequently asked questions
How often must a transformer station be inspected?
Annex 4 of Government Decree No. 190/2022 Coll. sets no separate interval for transformer stations. The interval is determined by the building and area (e.g. production 3 years, a building for more than 200 people 2 years, wet areas 1 year), otherwise by the environment under ČSN 33 1500 (indoor normal environment 5 years, outdoor 4 years). The shortest of the intervals affecting the equipment always applies, including a shorter interval set by the manufacturer.
Does the power have to be switched off for a transformer station inspection?
The external inspection and some of the checks can be done during operation. But insulation measurement, cable tests, inspection inside the cubicles and protection tests are done de-energised. We plan the shutdown to be as short as possible, if need be outside working hours.
Who arranges the shutdown with the distributor?
We do. We prepare the shutdown request, agree the date with the distributor and coordinate it with your operation. We need your consent and the supply point details from you. The shutdown has to be planned in advance, which is why we contact you in good time before the end of the interval.
How long does an HV inspection take?
It depends on the scope: a pole-mounted transformer station is different from a switchgear with several transformers and cables. The duration also depends on when and for how long the equipment can be switched off. We will tell you the expected duration in a non-binding quote.
What if the transformer station fails the inspection?
In the inspection report we state the faults with a reference to the violated provision and a proposed repair. Faults endangering safe operation must be removed without undue delay (Section 20(5) of Act No. 250/2021 Coll.). If safety is immediately endangered, the equipment must be disconnected. After the repair we verify that the faults have been removed and issue a new inspection report.
What is the difference between a periodic and an extraordinary inspection?
A periodic inspection is repeated at set intervals. An extraordinary one is carried out on the basis of a special requirement of a regulation, standard, authority or the owner of the equipment, for example after an accident, fire, flooding or when previous inspection reports are missing. The reason for an extraordinary inspection is stated in the inspection report.
Do you also inspect pole-mounted and kiosk transformer stations?
Yes. We inspect pole-mounted, kiosk and brick-built transformer stations, HV switchgear and switchboards, transformers, HV cables including tests, and overhead HV lines owned by the customer.
Who must have an HV inspection?
Everyone who operates designated high voltage electrical equipment: municipalities, companies, industrial sites, building managers and operators of PV plants with an HV connection. The only exemption is equipment of a licence holder's distribution system with a preventive maintenance plan (Section 21(1) of Act No. 250/2021 Coll.).