What Is a Voltage Drop?
Definition
The voltage drop is the difference between the voltage at the beginning and end of an electrical line. In an electrical network, the voltage can be reduced by the resistance and impedance of the lines, resulting in a lower voltage reaching the consumer than was originally fed in. This voltage loss is particularly relevant in long lines or with high loads and influences the efficiency and stability of a power supply network.
Voltage Drops in the Medium and High Voltage
In medium voltage (1 kV to 36 kV) and high voltage (36 kV to 150 kV), voltage drops can occur for various reasons. One of the main causes is high currents flowing through long lines, which leads to increased resistance and thus to voltage loss. This loss can occur particularly in rural areas where the distances between substations and consumers are large.
Other causes of voltage drops in the medium and high voltage can be:
- High load fluctuations: In times of high grid load, the voltage in the grid can drop.
- Poorly maintained lines or transformers that have higher resistances.
- Weather conditions, such as strong winds or storms, which can lead to line damage and thus to voltage drops.
The effects of these voltage drops can range from minor fluctuations in the power supply to serious grid faults. In extreme cases, a voltage collapse (blackout) can occur, which can jeopardize the entire grid operation.
REGSys®
Our »REGSys® voltage regulation system« is specially designed to compensate for voltage fluctuations and voltage drops in high and medium-voltage grids. In addition to the automatic regulation, monitoring and supervision of transformers with on-load tap-changers, REGSys® can be supplemented with additional functions such as current influence (e.g. compensation of line impedances) or parallel operation, depending on the individual application.
Voltage Drops in Low Voltage
In the low-voltage range (up to 1 kV), voltage drops occur for similar reasons as in medium and high voltage, although two causes of voltage drops are particularly common problems here:
- Voltage drops in parallel circuits when supplying several households via a common low-voltage line: If many consumers generate a high load at the same time – e.g. in the evening/night, during the typical charging times of electric vehicles – the voltage on the common lines can drop.
- Voltage drops due to long lines: The longer the line, the higher the resistance and therefore also the voltage loss. Especially in rural areas with long transmission lines, this cause often leads to a voltage drop.
In both cases, voltage drops can lead to problems such as failures, inefficient operation of electrical devices, increased energy consumption or even damage to sensitive devices.
LVRSys®
The »LVRSys® low-voltage control system« was specially developed to solve voltage stability problems in the low-voltage grid due to the integration of electromobility, photovoltaics and heat pumps or long transmission lines. It is an economical and flexible alternative to costly and time-consuming line extensions. The system is tried and tested, easy to integrate into the grid and maintenance-free.
Power Supply Guidelines for Energy Suppliers
Energy suppliers must comply with strict standards and guidelines to ensure a stable and reliable power supply. These standards define the permissible voltage drop and the permissible fluctuations in the grid voltage.
- Germany (national): In Germany, DIN EN 50160 applies, which specifies the permissible voltage drop for energy suppliers. It defines that the mains voltage must remain within a tolerance range of ±10 % of the nominal value.
- Europe (international): At European level, the EN 50160 standard also applies, which sets similar requirements for voltage quality.
- International standards: There are various standards around the world that specify the permissible voltage drop, including IEC standards (International Electrotechnical Commission). These standards vary from region to region, but the aim remains the same: to ensure a consistent voltage supply.
Overall, these guidelines are aimed at ensuring security of supply and preventing grid faults caused by impermissible voltage drops.
Where Do Voltage Drops Typically Occur?
Voltage drops can occur at various points in electrical networks, some common typical causes of voltage drops are:
Voltage Drop in Parallel Circuits
In parallel circuits, the current is divided into several paths so that the total resistance is lower than in a series circuit. Nevertheless, voltage drops can also occur here. In a parallel circuit, the voltage remains the same for all consumers, but the current is distributed over the individual branches, which can lead to voltage drops on the connecting lines in the case of high currents. An example of a voltage drop in parallel circuits is the supply of several households via a common low-voltage line. If many consumers draw electricity at the same time, the voltage on the common lines can drop (e.g. due to e-mobility and an increasing number of installed heat pumps).
Voltage Drop in Wires and Cables
The voltage drop in cables is one of the most common causes of voltage loss in electrical systems. The longer the line, the higher the resistance and the greater the voltage loss. This cause of voltage drop (line length) often leads to problems, especially in rural areas with long transmission lines.
- One example is the voltage drop in cables in the transmission or distribution network, particularly with high currents and long cable lengths. The cable cross-section plays a decisive role in this type of voltage drop, as a small cross-section leads to considerable voltage losses at high currents.
- In addition to the public power grid, voltage drop due to long cables can also occur in industry, where long cable runs are often required to operate machines and systems.
Voltage Drop Across Resistors in Electrical Supply Networks
A typical place where a voltage drop occurs is through the electrical resistance of components such as transformers, switches and loads. These resistors cause the voltage to drop when the current flows through them.
Examples of voltage drop across the resistor:
- Every load opposes the electric current with a resistance. The greater the resistance, the higher the voltage drop.
- In transformers, the winding resistance leads to voltage drops that reduce the output voltage.
- In switches and fuses, the contact resistance can cause additional voltage losses.
- In medium and high-voltage lines, voltage losses occur due to the ohmic resistance of the lines, especially over long transmission distances.
Short Insert – Calculating the Voltage Drop Across the Resistor
Ohm’s law is used to calculate the voltage drop across the resistor. This describes the relationship between voltage, current and resistance in an electrical circuit.
Formula:
Explanation of the variables
- ΔU: Voltage drop (in volts, V)
- I: Current flowing through the resistor (in amperes, A)
- R: Resistance of the component or cable (in ohms, Ω)
Calculation:
To calculate the voltage drop, multiply the current flowing through the resistor by the resistance value.
Example:
If a current of I=5 AI = 5, I=5A flows through a resistance of R=10 ΩR = 10, ΩR=10Ω, the voltage drop is calculated as follows:
The voltage drop across the resistor in this example is therefore 50 volts.
Voltage Drop Across Resistors in Direct Current and Alternating Current Systems
Voltage drops occur via resistors in both direct current and alternating current systems. In the direct current network, the voltage drop is directly proportional to the resistance, whereas in the alternating current network, the inductance and capacitance of the lines also play a role in addition to the ohmic resistance.
- With direct current, the voltage drop occurs in battery systems, for example. This typically occurs when the internal resistance of the battery impedes the flow of current.
- In the AC grid, both the ohmic resistance and the reactance of the lines influence the AC voltage drop, which leads to more complex voltage losses.
How Can a Voltage Drop Be Measured?
The voltage drop in an electrical network can be determined by directly measuring the voltage at various points in the system. To measure the voltage drop, the voltage at the beginning and end of a line, a circuit or upstream and downstream of a load is compared. The difference between the two voltage values corresponds to the voltage drop.
- To measure the voltage drop, the voltage is measured at two points simultaneously or consecutively, for example at the feed-in point and at the load.
- It is important that the measurement is carried out under load conditions, as the voltage drop only occurs when the current is flowing.
Measure Voltage Drop With a Multimeter
A simple tool to measure the voltage drop is the multimeter. A multimeter can accurately measure voltages in the low voltage range (< 1000 volts) and is often the first device used in smaller applications such as the installation or maintenance of electrical systems. To measure the voltage drop with a multimeter, the device is connected in parallel to the load and the voltage at the input and output of the circuit is measured.
- The multimeter is set to voltage measurement mode.
- The test leads are connected to the beginning and end of the cable or component to be tested.
- The voltage drop is calculated as the difference between the two measured values.
Measure the Voltage Drop at the Fuse
The voltage drop on fuses can be caused by the resistance of the fuse itself, unclean contact points or faulty installation. When the current flows through the fuse, the resistance causes a voltage drop, which is usually low, but increases when there is an overload or high current flow. To measure the voltage drop across a fuse, the multimeter is also connected in parallel to the fuse. By measuring the voltage before and after the fuse, it is possible to determine whether the fuse has a significant resistance and therefore causes a voltage drop.
Limits of Multimeters
Multimeters are useful for simple measurements, but have limitations when it comes to more complex analysis or monitoring grid operation. While you can measure the voltage drop with a multimeter, they are not able to provide detailed and more complex analysis and insight into the power quality or even record voltage fluctuations over a longer period of time. Multimeters have very limited functionality and only ever provide a snapshot of the current voltage.
Power Analyzers From A. Eberle – Highly Accurate and Powerful Devices That Can Do More Than Just Measure Voltage Drops
A more comprehensive and highly accurate analysis of the power quality as well as a more long-term view of voltage drops or voltage fluctuations for fault analysis and fault prevention is only possible through the use of power analyzers. Compared to multimeters, power analyzers from A. Eberle offer a wide range of functions that have been specially developed for the requirements of public and industrial power supply networks. They not only measure the voltage drop, but also provide information on voltage fluctuations, harmonics, flicker and other power quality parameters.
Some Advantages of A. Eberle Network Analyzers Over Multimeters
- Long-term monitoring: Grid analyzers from A. Eberle enable continuous monitoring of the grid and can record voltage fluctuations over longer periods of time, thus providing a meaningful insight into the grid quality at the measuring point.
- Fault records: Our permanently installed grid analyzers record transient faults and deviations in the grid current and voltage and generate a fault record diagram so that the causes of faults and their effects can be analyzed in detail (functionality depends on the selected order features).
- Power quality analysis: In addition to measuring voltage drop, our grid analyzers collect detailed data on voltage quality, which is particularly important in transmission, distribution and industrial grids.
- High precision: A. Eberle grid analyzers measure voltage drops and other grid anomalies with very high accuracy and provide data that is crucial for grid planning and optimization. All grid analyzers from A. Eberle are high-precision Class A measuring devices. The IEC 61000-4-30 Class A standard specifies power quality parameters for measurement methods, time aggregation, accuracy and evaluation. This ensures reliable, repeatable and comparable measurement results.
- Additional functions: In contrast to multimeters, our power quality analyzers offer the option of analyzing various grid parameters that indicate voltage problems, such as voltage fluctuations, harmonics, phase shifts, transients or flicker.
PQMobil – Our Mobile Network Analyzers
Reliably Detect Voltage Drops/Voltage Fluctuations and Mains Pollution Such as Harmonics, Flicker and Transients
The PQ-Box family consists of high-performance, portable mains and frequency analyzers, power meters and transient recorders for voltage monitoring and power quality measurement.
The focus during development was on user-friendliness and practical application. The devices are equipped with a wide range of trigger options to quickly localize the cause of grid faults.
All mobile power quality analyzers meet the high protection class IP65 and can also be installed and operated outdoors. The PQ boxes also have a very wide temperature range of – 20°C to + 60°C.
They also meet all the requirements of the measuring device standards IEC61000-4-30 Ed.3, IEC62586-1 and IEC62586-2 Ed.2 for class A devices.
PQSys – Our Permanently Installed Power Quality Network Analyzers and Fault Recorders
Be Prepared Today for the Requirements of Tomorrow
The permanently installed fault recorders and power quality network analyzers PQI-LV, PQI-DA smart, PQI-DE and PQI-D are the central components in a system that can be used to solve all measurement tasks in a low, medium and high-voltage network. The analyzers can be used as fault recorders with a sampling rate of up to 41 kHz, as power quality measuring devices in accordance with EN50160 / IEC 61000-2-2/4 or as power analyzers.
The components are suitable for monitoring and recording reference qualities or quality agreements between energy suppliers and their customers and making them available for evaluation or storage.
Modern power quality measuring devices work according to the IEC 61000-4-30 Ed. 3 standard. This standard defines measurement methods in order to create a comparable basis for the user.
How Is a Voltage Drop Calculated?
There are different formulas for calculating the voltage drop, which vary depending on the type of current – direct current, alternating current or three-phase current.
Basic formula for the voltage drop
The simplest formula for the voltage drop is based on Ohm’s law and is as follows
ΔU = I * R
Where:
- ΔU: the voltage drop (in volts)
- I: the current (in amperes)
- R: the electrical resistance of the wire or cable (in ohms)
This basic formula is particularly applicable for direct current applications and simple resistance networks. Additional factors must be taken into account for AC and three-phase networks.
Calculate Voltage Drop With Direct Current
To calculate the voltage drop with direct current, the formula ΔU=I⋅R\Delta U = I \cdot RΔU=I⋅R is used, whereby the resistance of the line or cable plays a significant role.
The following applies to the resistance RRR of a cable:
R = ( p * L ) / A
It says:
- ρ: specific resistance of the conductor material (in Ohm-mm²/m)
- L: Length of the cable (in meters)
- A: Cross-section of the cable (in mm²)
The complete voltage drop-direct current formula is therefore as follows:
ΔU = I * ( ( p * L ) / A )
Example: To calculate the voltage drop of a cable with direct current, the current in the cable, the length of the cable and the cross-section are used.
Calculate Voltage Drop for Alternating Current
The voltage drop for alternating current is more complex than for direct current, as the inductive and capacitive resistance (reactance) must be taken into account in addition to the ohmic component. The formula for the voltage drop for alternating current is
ΔU = I * Z
Here, Z is the impedance of the line and is determined by:
Z = √( R² + ( XL - XC )² )
It says:
- R: the ohmic resistance of the cable
- XL: the inductance of the cable (in ohms)
- XC: the capacitance of the cable (in ohms)
The impedance depends on the frequency and the electrical properties of the line, which makes it more difficult to calculate the voltage drop for alternating current. For many practical applications, the capacitive component is often neglected, so that the impedance is calculated as a combination of ohmic resistance and inductance.
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