In a large pot, heat 1/4 cup of the oil. Add the onion and cook over moderately high heat, stirring frequently, until softened, about 6 minutes. Add the garlic, ginger and curry powder and cook, stirring, until fragrant, about 2 minutes. Add the carrots and cook, stirring, for 2 minutes longer. Add the water and sugar and season with salt and pepper. Simmer over moderately low heat until the carrots are very tender, about 45 minutes.