PETROM EP Standard for Voltage and Earthing System

Onshore & Offshore.

Foreword

Scope

Range of applicability

Reference normative

General Assignations

Existent Voltage Levels

Recommended Voltages for New Projects

500 V, IT System

Typical use

System Implementation

Caution

Forbiddance

Requirements for Hazardous Areas

400/230 V, TNS System

Typical use

System Implementation

400/230 V, TT System

Typical use

System Implementation

400 V & 230 V, IT System, Offshore

Typical use

System Implementation

6 kV, IT System

Typical use

System Implementation

Foreword

The present standard has been developed having regards of the following:

Limits of international standardization

Complexity and, in some case, unusual existent voltage levels in PETROM E&P;

Various lessons learnt: equipment bought at inaccurate voltage level, which fail very fast or require additional devices, e.g. transformer.

Scope

The standard is intending to present the existing level of voltage used in PETROM E&P and recommendations for the new developments.

Voltages for special appliance are out of scope of this procedure:

100V (110V) used in automation and instruments / measurement & electrical protection;

660V level, used in drilling activity as intermediary voltage

DC voltage.

The voltages presented below are providing through Romanian National Grid (onshore).

Range of applicability

The standard applies to PETROM E&P, Onshore & Offshore, for the plants inside Romania's border.

Abroad the standard may be advisory only

Reference Normative

SR EN 61140:2002 Protection against electric shock - Common aspects for installation and equipment

SR EN 60 Safety of machinery - Electrical equipment of machines -- Part 1: General requirements

SR EN Marking of electrical equipment with ratings related to electrical supply. Safety requirements

SR HD 472 S1:2002  Nominal voltages for low-voltage public electricity supply systems

HD 384.3 S2:2004  Electrical installations of buildings. Part 3: Assessment of general characteristics

HD 60364-4-41:2007  Low-voltage electrical installations. Part 4-41: Protection for safety - Protection against electric shock

NP 099 Normative for electrical equipment in explosive atmospheres. (ID 17 revision)

NP-I7-02 Normative for design and execution of electrical installation with voltage up to 1000 V AC and 1500 V DC.

General Assignations

According to EN 60204-1, the equipment shall be manufactured to correct operates, between of specified voltage.

According to HD 472 S1, under normal system condition the voltage at the supply terminals should not differ from the nominal voltage by more than

Voltage sensitive equipment, as like as capacitors for power factor corrections or electronic devices, which are intended to use at 500V, in the step down transformer neighborhood, it's strongly recommended to be ranged at 550V-600V.

Frequency in National Electric System is 50 Hz according to standard for distribution.

The voltage shall be specified by qualified persons, after documentation on site.

Existent Voltage Levels

Main existent voltages are presented in table no. 1 and table no. 2

Table no. 1 Existent Low Voltage

Table no. 2 Existent Medium Voltages

Recommended Voltages for New Projects

The voltages from table no. 3 are recommended:

Table no. 3 Recommended Voltages for New Projects

*) Phase to phase;

**) Phase to Earth / Neutral

IT -insulated neutral (high impedance) / unearthed;

TT - neutral point (LV) earthed, metallic enclosure earthed.

500 V, IT System

Typical Use

Well pumps driver

Gas compressors motors drive;

Oil & water pumps in park.

System Implementation

The circuit is simple and cheaper using only 3 wires.

Reduced loses trough voltage (500V comparing to 400V)

Figure 1 shows a typical recommended 500 V, IT diagram

Figure 1

The basic feature of the IT system of earthing is that, in the event of a short-circuit to earth fault, the system can continue to operate without interruption. Such a fault is referred to as a "first fault".

In this system, all exposed conductive parts of an installation are connected via PE conductors to an earth electrode at the installation, while the neutral point of the supply transformer is either isolated from earth or connected to earth through a high resistance (commonly 1,000 ohms or more) at 50 Hz

This means that the current through an earth fault will be measured in milli-amps, which will not cause serious damage at the fault position, or give rise to dangerous touch voltages, or present a fire hazard. The system may therefore be allowed to operate normally until it is convenient to isolate the faulty section for repair work.

This enhances continuity of service

In practice, the system earthing requires certain specific measures for its satisfactory exploitation:

• Permanent monitoring of the insulation with respect to earth, which must signal (audibly or visually) the occurrence of the first fault
• A device for limiting the voltage which the neutral point of the supply transformer an attain with respect to earth
• A "first-fault" location routine by an efficient maintenance staff.
• Automatic high-speed tripping of appropriate circuit breakers must take place in the event of a "second fault" occurring before the first fault is repaired. The second fault (by definition) is an earth fault affecting a different live conductor than that of the first fault or a neutral conductor

The second fault results in a short- circuit through the earth and/or through PE bonding conductors.

This voltage is the most used throughout PETROM E&P to supply wells, parks and tanks farm: thousand transformer points, kilometer of OHL and thousand motors.

Caution

Many transformers, generic called as MT/0, 5 kV, have in fact the secondary voltage level at 525 V. In addition considering the behavior of Distribution Companies to work up to +10% over the MT nominal voltage results in a LV range at 550-600V which cause serious damage, especially to sensitive equipment as like as capacitors or electronics.

Some solution to avoid over voltage:

• Provide all transformers with tap changers for ±10%;
• Winding the defective transformers, when repair, at 500V;
• Order the sensitive equipment e.g. capacitors, at special voltage e.g. 550V
• Procedures for voltage monitoring and control [on hold]

Forbiddance

It is not allowed, for any reason, to buy equipment having nominal voltage lower than 500V, e.g. 400V, 440V or 480V.

Such equipment will be accepted only for testing purpose.

Final decision shall take into consideration the rise of cost and the decrease of efficiency caused by additional devices, e.g. transformers, but also the additional maintenance expenses. This decision shall be subject of written approval by Engineering Electrical Technical Authority

Requirements for Hazardous Areas

Existent Plants. Permanently Manned Facility.

IMD is mandatory and shall signal, acoustic and visual, the single phase fault. 

Allowable operation time, with a single phase fault shall not exceed 6 (six) hours if is not otherwise specified by plant designer.

Existent Plants. Unmanned Facility.

IMD is mandatory and shall signal local the single phase fault. 

Inspection / Operation Teams shall check the signal and report according to maintenance procedure [on hold

Fault localization and elimination shall not exceed 10 (ten) hours if is not otherwise specified by plant designer.

New Permanently Manned Plants.

IMD is mandatory and shall signal, acoustic and visual, the single phase fault.

Trip and remote communication are recommended.

Allowable operation time, with a single phase fault shall be specified by plant designer, according to maintenance procedure [on hold

New Unmanned Plants.

IMD is mandatory and shall signal local the single phase fault. 

Remote communication is strongly recommended.

Allowable operation time, with a single phase fault shall be specified by plant designer, according to maintenance procedure [on hold

400/230 V, TNS System

Typical use

• Offices, Home appliance and similar.

System Implementation

Figure 2 shows a typical recommended 400 V, TN-S system

Figure 2

400/230 V, TT System

Typical use

Industrial appliance. Facilities: Parks, Tank Farms, Gas Compressor Stations, Water Injection Stations.

System Implementation

Figure 3 shows a typical recommended 400 V, TT system

R_A x I_Dn ≤ 50V

R_A and ID are defined and calculated as per standard HD 60364-4-41

Figure 3

V & 230 V, IT System, Offshore

Typical use

Offshore

System Implementation

Figure 4 and 5 shows a typical recommended 400 V / 230 V, IT systems

Figure 4

Figure 5

6 kV, IT System

Typical use

Motors drive larger than 160kW, gas& air compressors and water injection pumps.

System Implementation

Figure 6 shows a typical recommended 6 kV, IT system

Figure 6