VT Ratio Calculator: Voltage Transformer Primary & Secondary

VT Ratio Calculator

Calculate the VT secondary voltage from the primary voltage or find the required VT ratio for your system. Includes formulas, tables, and examples for easy conversion.

voltage transformer ratio formula

The ratio of the VT is used to denote the process of reducing a high primary voltage down to a standard secondary voltage. Calculate it by the formula: Vs = Vp(Ssec/Pvt) in which Vp is the primary voltage, Pvt is the VT primary rating, and sec is the secondary voltage rating. The proper choice of VT ratio allows safe and proper metering and protection in an electrical system.

Formula & Table Summary:

Secondary Voltage: V_s = V_p × (S_sec / P_vt)
Required VT Primary: P_vt = V_p × (S_sec / V_s)
Primary-Equivalent from Measured Secondary: V_p_eq = V_s × (P_vt / S_sec)

Converter Table (Input → Output):

Input	Formula	Output
VT ratio & Primary Voltage	V_s = V_p × (S_sec / P_vt)	Secondary Voltage
Primary Voltage & Desired Secondary	P_vt = V_p × (S_sec / V_s)	Required VT Primary
Measured Secondary & VT ratio	V_p_eq = V_s × (P_vt / S_sec)	Primary-Equivalent Voltage

vt primary secondary conversion

Voltage Transformer (VT) ratios reduce high primary voltages to standard secondary voltages (e.g. 110 V or 120 V) to be used in metering and protection. The VT ratio is indicated as Primary / Secondary, e.g. 11 kV / 110 V. To compute secondary voltage, primary voltage multiplied by secondary rating/VT primary rating. The proper ratio of VT is selected to make the measurements correct and in order to prevent overload of metering circuits. The guide will include formulas, converter tables, the sample calculation, low-competition keywords, image metadata, FAQs in the JSON format, and ready TailwindCSS parts to be implemented immediately. The VT ratio calculator enables electrical engineers, technicians and students to compute secondary voltages with safety and accuracy with respect to primary systems.

voltage transformer calculator

Scenario	Input	Calculation	Result
Example A	VT 11kV/110V, V_p = 5.5 kV	V_s = 5.5 × 110 / 11000	55 V
Example B	VT 33kV/110V, V_p = 16.5 kV	V_s = 16.5 × 110 / 33000	55 V
Choose VT	V_p = 22 kV, desired V_s = 110 V	P_vt = 22 × 110 / 110	22 kV recommended
Back-Calc	Measured V_s = 100V, VT 11kV/110V	V_p_eq = 100 × 11000 / 110	10 kV

Frequently Asked Questions - VT Ratio Calculator:

What does a VT ratio mean?

VT ratio Primary/Secondary shows how primary voltage is stepped down to a standard secondary (e.g., 11kV/110V).

How to get VT secondary voltage?

V_s = V_p × (S_sec / P_vt). Example: VT 11kV/110V, V_p 5.5kV → V_s = 55V.

What are common VT secondary ratings?

110 V and 120 V.

How to choose VT primary rating?

Pick VT primary ≥ expected max primary voltage and standard secondary (110/120V). Round up to next standard.

How to compute primary-equivalent from measured secondary?

V_p = V_s × (P_vt / S_sec).

Why choose 110V vs 120V secondary?

Depends on metering standard; 110V is common in older systems, 120V in modern circuits.

What happens if VT is overloaded?

VT can saturate and give inaccurate readings; never open-circuit secondary under load.

Can VT ratio be fractional?

VT ratios are typically whole numbers; fractional secondary voltages arise if primary voltage isn’t exact multiple.

How to handle multiple primary turns?

Effective primary = N × voltage; formula applies using effective primary voltage.

Where to find VT standard sizes?

Refer to VT manufacturer catalogs; common primaries: 11, 22, 33 kV etc.

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VT Ratio Calculator: Voltage Transformer Primary & Secondary

VT Ratio Calculator

VT Ratio Calculator

voltage transformer ratio formula